Joe Burchenal and the birth of combination chemotherapy

Joe Burchenal and the birth of combination chemotherapy

Angela Thomas

Department of Haematology, Royal Hospital for Sick Children, Edinburgh, UK.

Summary

When Joe Burchenal started studying medicine at the Univer-

sity of Pennsylvania in 1934, antibiotics had not been

discovered and the survival of patients diagnosed with acute

leukaemia was <4 months. By the time he retired in 1983, 58%

of children with acute lymphoblastic leukaemia survived

5 years with the majority being cured of their disease. His

early work in infectious diseases and antimicrobials equipped

him well, both clinically and scientifically. The approach to

developing antibiotics to conquer previously incurable

infection was an inspiration and model for his pioneering

work when searching for drugs with activity against cancer.

Trials of sequential and then combination chemotherapy

followed. Success in treating lymphoid malignancies in

children led him to develop treatment regimens for other

more resistant cancers, and as an advocate of collaborative

working he introduced multimodal therapy to tackle bulky or

metastatic cancers, replacing inevitable relapse with a chance of

true cure.

Keywords: Burchenal, acute leukaemia, combination chemo-

therapy

Joe Burchenal was born in Milford, Delaware in 1912 and was

interested in chemistry even as a young boy, trying to make

gunpowder with his cousin using a rudimentary chemistry set

and assorted kitchen ingredients. His interest in chemistry was

carried through his school years at Exeter Academy, New

Hampshire and he decided on a career in medicine, studying

initially at Princeton followed by his clinical studies at the

University of Pennsylvania. He passed out of each institution

with, in his words, ‘gentleman’s grades’ but with a particular

interest in chemicals and their possible use in curing infectious

diseases. He wondered too, whether, if infectious disease

proved treatable, it might be possible to treat cancer with

chemicals. Not all shared his optimism: a bacteriology

instructor pointed out that mercurochrome, a useful topical

antiseptic compound, when injected into patients with blood-

borne infection, killed the patient along with the bacteria

(Laszlo, 1995).

His first experience with cancer was personal, when his

stepmother was diagnosed as having osteogenic sarcoma of her

leg while in his first year at Princeton. Despite amputation, she

died 2 years later from metastatic disease to the lung. While at

medical school, Burchenal had seen the introduction of

Prontosil, a dye with antibacterial properties from which the

sulpha compounds were developed. This was being used

successfully to treat meningitis and streptococcal infection. To

Burchenal, the conquest of infectious disease suggested that the

conquest of cancer could also be accomplished. During his

training, he went to the Union Memorial Hospital in

Baltimore, attached to the paediatric service. There he met

his first patients with acute leukaemia and was able to review

their blood films under the guidance of the haematologist Dr

Walter Baetjer. He continued his postgraduate training in New

York where, as well as clinical studies, he was able to

participate in mouse leukaemia experiments with Dr Jacob

Furth and continue with further morphology teaching. His

interest in haematology and leukaemia led to a recommenda-

tion that he work with Dr George Minot and Dr William

Castle at the Thorndike Laboratory at Boston City Hospital

where a cure for another previously fatal blood disorder,

pernicious anaemia, had been discovered. George Minot, along

with William Murphy and George Whipple shared the Nobel

Prize in 1934 for Medicine or Physiology for identifying the

missing red cell maturation factor, vitamin B12, in pernicious

anaemia. In this work, an important concept was appreciated –

that minute amounts of a chemical could profoundly influence

the workings of a cell.

Burchenal delayed going to Boston in order to go to Europe

with the intention of working in a number of laboratories in

Germany and France. However, World War II broke out and

he had to stay in Switzerland where he happened to be on

holiday at the time. This gave him the opportunity to work

with two eminent Swiss haematologists: Dr Fanconi, with

whom he worked on children’s cancers and leukaemias, and Dr

Karl Rohr, under whose guidance he learnt how to interpret

bone marrow aspirates. The technique of bone marrow

aspiration was new and was just being utilised by two leading

British doctors working in haematology: Sir John Dacie

introduced aspiration biopsy to Manchester in 1936 and its

use formed the basis of Sir Ronald Bodley Scott’s MD thesis in

Correspondence: Angela Thomas, Department of Haematology, Royal

Hospital for Sick Children, Sciennes Road, Edinburgh EH9 1LF, UK.

E-mail: [email protected]

historical review

ª 2006 The AuthorsJournal Compilation ª 2006 Blackwell Publishing Ltd, British Journal of Haematology, 133, 493–503 doi:10.1111/j.1365-2141.2006.06072.x

1937 (Christie & Tansey, 2003). Late in 1939, Joe Burchenal

heard from Dr Minot in Boston again, offering him a short-

term position with the Harvard group. Burchenal accepted and

was able to teach the group how to perform sternal bone

marrows, because the analysis of such samples would be

essential for their research. He made his own bone marrow

needles from lumbar puncture needles and offered himself as

the first normal subject so that his fellow researchers could

practice the technique; apparently, it was a bit painful.

While Minot’s and Castle’s work on vitamin B12 was

continuing, D.D. Woods and Paul Fildes, of the Bland Institute

of Pathology in London, were attempting to answer the

question of how the sulphonamides that had been developed

from Prontosil worked. Consistent with Minot’s and Castle’s

work was the hypothesis that cells require specific chemicals to

function. It had been shown from their work and others that

human cells needed specific vitamins and Woods and Fildes

suggested that bacterial cells had a requirement for specific or

essential metabolites. They showed that the sulphonamides

worked by mimicking and consequently blocking the essential

metabolite para-aminobenzoic acid (Woods, 1940). From this

theory of anti-metabolites, came the notion of anti-metabolites

for treatment of malignant disease (Fildes, 1940). This theory

stimulated the classic, systematic studies of antagonists of the

naturally occurring purines and pyrimidines. This work was

started in 1942, by George Hitchings at the Borroughs

Wellcome Company in Tuckahoe, New York, USA, even

though very little was known about DNA and its true role

within a cell apart from the fact that it was essential for

replication. Hitchings tested his new drugs using the bacterium

Lactobacillus casei, which required both a purine (A or G) and

thymine (T) to grow. Gertrude Elion joined Hitching’s group

in 1944 and by 1951 had synthesised and tested over 100

modified purines. The compounds that slowed or prevented

the growth of L. casei were studied further. Eventually, they

had a number of chemicals ready to be tried in human disease.

It is interesting to note that their laboratory was partly

financed for many years by the Sloan-Kettering Institute,

despite the fact that it was situated in Burroughs Wellcome

American research headquarters (Christie & Tansey, 2003).

At the time of the work on anti-metabolites, it was apparent

that folic acid was essential for cell growth and formation of

blood. Leuchtenberger et al (1944) postulated that folic acid

might be able to mature other cells, such as malignant cells,

and this led to trials to see if folic acid might be useful in the

treatment of leukaemia. Folic acid was first synthesised in 1945

(Angier et al, 1945) and several people began using it in

patients with acute leukaemia. One of these was Sidney Farber,

a paediatric pathologist in Boston, who launched a clinical trial

in 1947 testing folic acid congeners in adults and children with

malignant tumours (Farber et al, 1947). Along with two other

independent researchers, he noted that the leucocyte count

rose, and interpreted this as an acceleration of the leukaemic

process. He therefore enlisted the help of a colleague, a

biochemist Dr Yella Subba Row, who led the Research Division

of the Lederle Laboratories of the American Cyanamid

Company, to synthesise conjugates of folic acid and its

analogues. It was found that some of these compounds had

anti-leukaemic properties and Sidney Farber used aminopterin

(4-aminopteroyl-glutamic acid) in 16 patients with acute

leukaemia; 10 of them achieved complete remission (Farber

et al, 1948). The remissions were brief but this was an

encouraging start and proved that a simple chemical com-

pound could be effective against acute leukaemia.

In 1940 during his time in Boston, Burchenal set his research

into cancer aside and took a reserve commission in the army

with the Fifth General Hospital, the ‘Harvard Unit’. Once the

US had entered the war in 1942, he was sent first to Northern

Ireland and then to Salisbury in England. Here he gained

valuable experience in the treatment of infectious diseases and

in 1944, just after the D-Day landings, went on to set up an

infectious disease ward in Normandy, which was really just a

group of hospital tents isolated from each other. Soon after

this, his wife died unexpectedly and he returned to the States.

He had an opportunity to attend a 3-month tropical diseases

training course at the Walter Reed Army Hospital in Wash-

ington D.C. and he finished first in the class. Because of his

specialised work, Burchenal had access to the resources at the

Army Institute of Tropical Medicine and heard about work in

another area, that of chemical warfare. The compounds that

were being studied were the nitrogen mustards, the nitrogen

analogues of mustard gas that had been used in the First World

War. The studies of Krumbhaar and Krumbhaar (1919)

showed that soldiers were dying of bone marrow aplasia from

exposure to sulphur mustard gas. During World War II,

research in both the US and in Britain showed that the

nitrogen mustards produced marked effects in the haemato-

poietic system. Exposure to the nitrogen mustard code-named

HN2 resulted in severe damage to the lymphoid organs and

bone marrow. This led several researchers to try the chemical

first in mouse lymphosarcoma and then in patients with

lymphoma; significant therapeutic effects were observed

(Goodman et al, 1946; Rhoads, 1946; Wilkinson & Fletcher,

1947). Unfortunately, because of the Official Secrets Act

neither the American nor the British researchers were able to

publish the work that commenced in 1941 until 5 or 6 years

later, but subsequently were able to work closely together. One

such researcher was Cornelius P. (Dusty) Rhoads, who had

headed the medical division of the US Chemical Warfare

Service but had left to set up a new cancer research unit at

Memorial Hospital in New York. Although Burchenal was

offered a post with the Chemical Warfare Service, he declined

as Rhoads was looking for someone to do research on both

human leukaemia and experimental leukaemia in mice and

this was precisely the sort of post that he wanted. He started as

a Special Fellow in Medicine at Memorial Hospital, New York

in 1946 and as an Associate Member of the Sloan-Kettering

Institute when it opened in 1948 (Fig 1). The Institute

included an Experimental and Clinical Chemotherapy Division

where, in addition to Dr Rhoads, other colleagues included Dr

Historical review

ª 2006 The Authors494 Journal Compilation ª 2006 Blackwell Publishing Ltd, British Journal of Haematology, 133, 493–503

David Karnofsky, Dr C. Chester Stock and Dr Fred Philips

(Fig 2). They had worked together in the army and now, in

New York, had the chance to transfer their wartime research

into peaceful application. They became a formidable group of

leaders in the field of cancer chemotherapy.

In 1947, the group became aware of Sidney Farber’s work

with aminopterin in Boston and Burchenal travelled to his unit

to see the results of its use in acute leukaemia first-hand.

Having been convinced that the drug did indeed produce

complete remission, the Memorial group obtained some of the

drug, as yet unlicensed, for trials in their own patients. The

first nine children who were treated showed no response but

the tenth went into remission (Laszlo, 1995). Prior to this,

acute leukaemia was a fatal disease unresponsive to drugs, so

although there was only a single response in their patients it

encouraged the group to look at other anti-metabolites. This

was enabled by collaboration with Hitchings and Elion. The

cooperative project between Hitchings and his co-workers and

Burchenal and his team had two main objectives: to obtain

fundamental knowledge of the roles of purine and pyrimidine

bases in growth and of the part played by folic acid in the

synthesis of these bases and to uncover effective chemothera-

peutic agents against neoplastic disease (Fig 3). By 1948,

Hitchings and Elion had synthesised a chemical 2,6-diamin-

opurine, which had two amine groups protruding from the

normal purine structure and blocked the incorporation of

adenine into DNA. They sent this compound to Joe Burchenal

for testing, initially in mice and then in humans. He managed

to achieve two remissions in adults with leukaemia but the

drug caused intolerable nausea and vomiting for most patients.

Elion therefore modified this first compound by replacing an

oxygen atom on the purine ring with a sulphur atom. This

chemical, 6-mercaptopurine (6MP), was then tried in mice

against Sarcoma 180 where it not only inhibited growth of this

tumour but also caused a significant percentage of the tumours

to regress permanently (Clarke et al, 1953). It was also shown

to be effective in prolonging the survival time of mice

Fig 1. Memorial Sloan-Kettering in 1970. Reproduced by courtesy of

Memorial Sloan-Kettering.

Fig 2. Dr Rhoads discusses chemotherapy with (left to right) Dr Fred Philips, Dr John Biesele, Dr H. Christine Reilly, Dr Joseph Burchenal, Dr C.

Chester Stock, Dr David A. Karnofsky and Dr George W. Woolley. Photographer: Ike Vern c. 1956. Reproduced by courtesy of Memorial Sloan-

Kettering.

Historical review

ª 2006 The AuthorsJournal Compilation ª 2006 Blackwell Publishing Ltd, British Journal of Haematology, 133, 493–503 495

inoculated with transplanted leukaemia, in strains both

sensitive and resistant to the folic acid antagonist A-methop-

terin (methotrexate), which had succeeded aminopterin. Fred

Philips then studied the drug in dog models, determining the

maximum tolerated dose, mode of delivery and the drug’s

toxicities, which were predominantly bone marrow hypoplasia,

diarrhoea, gut toxicity and hyperbilirubinaemia. These toxici-

ties were reversible but could not be prevented as they had

been in the L. casei system by the addition of nucleic acids. In

addition, occasional remissions had been noted with this drug

in human leukaemia (Burchenal et al, 1951a). Finally, 6MP

was ready for clinical trial.

At the same time as this research, further work was being

carried out on prevention of toxicity and drug resistance, as it

was possible that these were linked. Citrovorum factor, now

known as folinic acid, had been shown to be a more effective

inhibitor of aminopterin and methotrexate than pteroyl-

glutamic acid (PGA). Pretreatment of mice with folinic acid

allowed large doses of aminopterin or methotrexate to be given

but it was found that the protective effect was lost if given 4 h

later. It was also noted that it prevented the anti-leukaemic

effects of methotrexate in mice and therefore was unlikely to be

of any practical use in the treatment of acute leukaemia in

children (Burchenal & Babcock, 1951). Later, after more

experience with use of the drugs had been gained, folinic acid

was used successfully to ‘rescue’ patients from the effects of

high doses of methotrexate without loss of efficacy (Djerassi

et al, 1968). Burchenal also showed that an aminopterin-

resistant strain of mouse leukaemia that he developed was

resistant to all other 4-amino derivatives of PGA tested but not

to 2,6-diamino-purine (Burchenal et al, 1951b). Extending this

work, he looked at the effect of steroids on sensitive and

resistant transplanted leukaemias in mice. He had already

noted that cortisone did not cause prolonged survival in these

mice but that a single large dose produced a fall in the

leucocyte count in advanced disease and that this occurred in

both methotrexate-sensitive and methotrexate-resistant

strains, again showing lack of cross-resistance with different

anti-leukaemic agents (Burchenal et al, 1951c). These results

suggested that using different agents without cross-resistance

might be beneficial in prolonging survival. In the 30–50% of

children who initially responded to methotrexate, treatment

failure was usually because of development of resistance. Even

so, methotrexate could prolong survival to 14–16 months.

Forty to 60% of children responded to cortisone, but the

response was very short-lived, just 1–2 weeks. It was also

observed that if the white cell count was high, >50 · 109/l, or

the child was very sick, pre-treatment with steroids [adreno-

corticotrophic hormone (ACTH) or cortisone] was beneficial

before methotrexate was started (Dargeon & Burchenal, 1951).

If resistance to methotrexate developed, sometimes sensitivity

could be regained after a course of steroids.

It was clear that in order to be able to evaluate the effects of

treatment, the natural history of the leukaemias and their

epidemiology needed to be established. A reliable system for

classification was needed; initially chronic myeloid and lym-

phatic leukaemias were described but there was no distinction

between acute myeloid and acute lymphoblastic leukaemias.

Individual drugs were being identified as having a therapeutic

effect and, in order to compare response, agreed descriptions

Fig 3. Dr Burchenal discussing new chemical compounds with Dr Chester Southam and Dr Marguerite Sykes with whom he performed the first trials

with 6-mercaptopurine. Photograph c. 1956. Reproduced by courtesy of Memorial Sloan-Kettering.

Historical review


of response were required. The Clinical Studies panel of the

Cancer Chemotherapy National Service Center agreed and

published criteria for evaluation of response to therapy (Bisel,

1956). These included assessment of bone marrow, peripheral

blood, physical findings and clinical symptoms and were

adopted by Burchenal prior to the publication. Bone marrow

remission was defined as blasts and lymphocytes forming

<30% of nucleated cells in the bone marrow and the normal

erythroid and myeloid elements increasing to at least 70% with

megakaryocytes present. Peripheral blood remission required

satisfactory blood counts that were a little lower than the

normal range for age and absence of leukaemic cells. Later, it

was realised that failure to achieve complete remission in the

peripheral blood because of low counts despite a full remission

in all other domains was probably because of the chemother-

apy itself. Karnofsky then developed a clinical score of well-

being and activity for adults, the Karnofsky score, which was

more relevant clinically and enabled better analysis of results.

Burchenal and his colleagues reviewed 172 cases of leukaemia

seen at the Memorial Hospital from 1926 to 1948 (Southam

et al, 1951). Of those patients under 15 years of age, 62 were

boys and 33 were girls, giving a ratio of 1Æ9:1. Diagnosis wasmade on the basis of morphology alone and 49 were cases of

acute lymphoblastic leukaemia, 22 acute myeloid leukaemia

and 24 were unclassified. In the patients who were aged

‡15 years, the ratio of myeloid to lymphoblastic leukaemia was

reversed, with 45 having acute myeloid leukaemia and 20 acute

lymphoblastic leukaemia. Twelve patients had an unclassified

acute leukaemia and the ratio of males to females was 2Æ1:1.Twenty-two cases had been treated with folic acid antagonists

and these were excluded from the data on remission. Of the

remaining 150 patients, 8Æ7% experienced some degree of

temporary remission but only 4Æ0% had complete temporary

remission. These were not related to episodes of infection or

preceding treatment (see below). No patient achieved a second

remission. The mean survival time from onset of symptoms

(not from diagnosis) was 20Æ3 weeks; the longest survival was

58 weeks but 50% of patients were dead within 17 weeks and

90% by 36 weeks. The mean survival time was calculated in

this way for several reasons. It was recognised that this was not

a precise measure of the duration of the pathological process

and it was appreciated that this time did not necessarily reflect

how long haematological changes might have existed before

symptoms occurred. It was also recognised that, in a few

asymptomatic patients, the diagnosis was made on a routine

blood count. However, other methods of estimating survival

duration were deemed even less precise both because diagnosis

may have been delayed and treatment, such as X-ray therapy,

nitrogen mustards, radioactive phosphorous and urethane,

were all without significant effect. The slight but significant

increase in survival time that was seen over time was attributed

to improved supportive measures, such as antibiotics and

generous use of blood transfusions. It is interesting to note that

no spontaneous remissions were seen in association with blood

transfusion. Hayhoe reported, in the first paper of the first

volume of the British Journal of Haematology, his experience of

giving fresh blood transfusions to patients. A number of their

patients achieved a complete, but short-lived, remission

(Hayhoe & Whitby, 1955).

Burchenal’s clinical trial using 6MP was a turning point

(Burchenal et al, 1953), just as Farber’s trial of methotrexate

was 5 years earlier (Farber et al, 1948). At the onset of the

clinical study, 6MP was given to several patients with far

advanced cancer to obtain the dosage tolerated by man. This

was found to be around 2Æ5 mg/kg/d with the drug given

orally. Escalation of dose within the clinical trial to maximum

tolerated dose was planned unless a therapeutic response was

achieved before this dose was reached. It was noted as the trial

progressed that improvement often occurred without toxicity

in patients with leukaemia but in most patients with other

types of tumours, toxicity was apparent without any thera-

peutic response. The initial starting dose in most patients was

2Æ5 mg/kg with the dose rounded to the nearest 25 mg. While

in the hospital, patients had daily white cell count and

haemoglobin measurements; platelet and reticulocyte counts

were taken weekly, often with hepatic and renal function tests.

This starting dose was continued for 4 weeks and if there was

no clinical improvement or definite evidence of a fall in white

cell count, the dose was doubled to 5 mg/kg. Many patients

were well enough to be followed as outpatients and their blood

samples were monitored weekly. Patients on active treatment

also had weekly bone marrow aspirates and once remission was

achieved, aspirates were performed every 2 weeks. In this way,

107 patients were entered into the trial between April 1952 and

March 1953, of whom 93 were considered to have received an

adequate course of 6MP (at least 3 weeks) and were evaluable.

Table I. Diagnoses and number of patients treated with 6-mercapto-

purine.

Diagnoses Total number

Number receiving

adequate trial

Acute leukaemia

Children 45 43

Adults 18 14

Subacute and chronic

myelocytic leukaemia

6 6

Chronic lymphatic leukaemia 3 3

Hodgkin disease 5 5

Reticulum cell sarcoma 2 2

Miscellaneous cancers

Children 11 8

Adults 17 12

Total 107 93

Adapted from research that was originally published in Blood. Bur-

chenal, J.H., Murphy, M.L., Ellison, R.R., Sykes, M.P., Tan, T.C.,

Leone, L.A., Karnofsky, M.D., Craver, L.F., Dargeon, H.W.& Rhoads,

C.P. (1953) Clinical evaluation of a new antimetabolite, 6-marcapto-

purine, in the treatment of leukaemia and allied diseases. Blood, 3, 965–

999. � the American Society of Hematology.

Historical review


The diagnoses and number of patients treated with 6MP are

shown in Table I. The most important toxic effect was that of

bone marrow depression and resultant pancytopenia. The drug

was therefore interrupted when the white cell count showed a

fall and treatment was restarted when the counts had been

stable for a few days or had begun to rise. Bone marrow

aspirates done at the same time sometimes showed hypoplasia

but could also be normocellular. The megaloblastic change

reported with the folate antagonists was not seen. Bone

marrow recovery was usually prompt after cessation of 6MP.

In addition to the toxicities already mentioned, patients with

high white cell counts or extensive lymphoma occasionally

developed hyperuricaemia with temporary renal impairment

and oliguria. It was presumed that this was due to rapid

destruction of tumour tissue and seemed to respond to

alkalinization and forced fluids.

The results showed that 15 of 45 children with acute

leukaemia achieved good clinical and haematological remis-

sions with 6MP after 2–9 weeks of therapy and which lasted

between 2 and 22 weeks. A further 10 patients showed partial

remissions and clinical improvement. Four children had their

treatment ‘complicated’ by steroid therapy or methotrexate

and two children died within 2 weeks of treatment. Eight of

the 15 who achieved complete remission and four of the 10

who achieved partial remission had had no previous therapy.

Although there were 14 children in whom the treatment failed

and 13 had shown resistance to both folate antagonists and

steroids, importantly it was shown that 6MP was effective in

children whose disease was resistant to the folic acid

antagonists. Twenty-four children in the trial with acute

leukaemia had disease resistant to methotrexate yet five had

good clinical and haematological remissions with 6MP and

five had partial remissions. Some benefit was seen in eight of

18 patients whose disease was resistant to ACTH or cortisone.

There was some evidence too that resistance to 6MP

developed more rapidly than resistance to the folic acid

antagonists but there did not seem to be any laboratory or

clinical evidence of cross-resistance. Although the mode of

action of 6MP was not known precisely, it was recognised that

it appeared to differ from the other active agents in acute

leukaemia and, as such, was of fundamental as well as clinical

interest. It was also noted that partial and complete remis-

sions from bone marrow analysis were clinically indistin-

guishable. This observation led to the practice of frequent

bone marrow analysis with change of medication from one

class of drug to another when resistance was evident by

increasing numbers of bone marrow blasts. Occasional

remissions were achieved in adults, although at this time no

distinction was made between acute myeloid and acute

lymphoblastic leukaemia. Response was also seen in both

the early and late stages of chronic myelocytic leukaemia.

Conversely, in a total of 35 patients with lymphomas and

miscellaneous carcinomas and sarcomas, no definite clinical

improvement was seen at doses that produced significant

haematological toxicity (Burchenal et al, 1953).

When the news of the success of 6MP in treatment of acute

leukaemia broke, Hitchings received hundreds of phone calls.

The United States Food and Drug Administration (FDA)

approved its use in late 1953, only months after the first year’s

results of the clinical trial were available. Such rapidity with

licensing has only been matched in recent years when STI157

gained its licence for treating chronic myeloid leukaemia

within 3 months of submission of the registration papers

(Christie & Tansey, 2003).

Following on from this study, 6MP was evaluated in a

further 269 patients having various forms of neoplastic disease

(Burchenal et al, 1954a). This confirmed that 6MP produced

remissions in both adults and children with acute leukaemia.

Of the 87 children having acute leukaemia in this study, 41

(47%) had good clinical and haematological remissions and 16

children (18%) had partial remissions even though more than

50% of patients had disease resistant to methotrexate, steroids

or both. Conversely, of the 37 children whose disease was

initially responsive but then resistant to 6MP, 14 responded to

methotrexate. It was therefore recognised that in acute

leukaemia there were three types of active agent: the folic acid

antagonists, the purine antagonists and steroids. Lack of cross-

resistance between the classes had been established, both in the

laboratory and clinically and the differences in speed of action

and duration of remission had been observed. Burchenal

concluded that methotrexate and 6MP should be the mainstay

of treatment of the acute leukaemias with steroids kept for

emergency situations where the disease had become resistant to

the other two drugs or where there was not sufficient time for

the use of these slower acting drugs. When used in sequence,

these drugs gave a definite increase in survival time (Table II).

The study also confirmed the lack of efficacy of 6MP in

treating metastatic carcinomas, sarcomas, Hodgkin disease,

lymphosarcomas and chronic lymphocytic leukaemia and that

it produced a high percentage of ‘remissions’ in the early stages

of chronic myelocytic leukaemia. In patients with myelo-

monocytoid or monocytic leukaemia and in adults over the age

of 40 years occasional responses were seen.

During this trial, the notion of combination therapy was

considered. Previous studies had shown no synergism of 6MP

with methotrexate or cortisone. However, some synergism had

Table II. Sequential therapy of acute leukaemia in children.

Patients

Surviving 1 year

or more (%)

No treatment 218 5

Folic acid antagonists and/or cortisone 154 29

Folic acid antagonists, cortisone and 6MP 52 52

Adapted from: Burchenal, J.H., Ellison, R.R., Murphy, M.L., Karnof-

sky, D.A., Sykes, M.P., Tan, T.C., Mermann, A.C., Yuceoglu, M, Myers,

W.P., Krakoff, I.& Alberstadt, N. (1954a) Clinical studies on 6-mer-

captopurine. Annals of the New York Academy of Sciences, 60, 359–368,

with permission from Blackwell Publishing.

Historical review


been demonstrated between 6MP and a new drug Azaserine

(O-diazoacetyl-l-serine) in Sarcoma 180 and subsequently

confirmed in mouse leukaemia (Burchenal et al, 1954b; Clarke

et al, 1954). A preliminary study with three arms was initiated

in children with acute leukaemia: one group of patients was

started on the combination from the beginning of their disease;

a second group was in remission on maintenance therapy with

6MP and had azaserine added in and the third group had

disease resistant to 6MP when the combination was started. In

the first group, 14 of 19 patients achieved a good clinical and

haematological remission and two partial remissions lasting

from 12 to 35 weeks. Although this was an improvement in

remission status on 6MP alone it was noted that the patients

were selected as those being well enough to have a reasonable

trial of therapy. The second group of 15 children showed a

slight but probably not significant increase in remission over

6MP alone. Six children in the third group had very temporary

remissions, with nine not responding at all, showing that

azaserine was not of much practical value in this situation.

However, two patients were treated with steroids as their

disease either worsened or relapsed on 6MP and then started

on 6MP and azaserine in combination, remaining in remission

for a further 10 months each (Fig 4). These results encouraged

Burchenal and his colleagues to perform the first randomised

study comparing a single agent, 6MP, with a combination 6MP

and azaserine.

The Leukaemia Chemotherapy Cooperative Study Group A,

which was organised under the guidance of the Clinical

Studies Panel of the Cancer Chemotherapy National Service

Center, undertook a randomised trial of comparison of 6MP

with the combination of 6MP and azaserine in the treatment

of acute leukaemia in children (Heyn et al, 1960). Two

hundred and fifty cases were recruited from December 1955 to

March 1957 by the 11 investigating institutions, of which the

Memorial Center New York was one. Many patients were

excluded, including those who received fewer than 4 weeks of

therapy or those who had received initial steroid therapy due

to poor clinical state. As a result, only 125 patients were

analysed and these cases therefore were selected to be less

severe than the total population. The overall results were

disappointing, in that, although complete remission rates were

44Æ8% for 6MP alone, the results were not significantly better

for the combination, at 48Æ3% and overall survival was no

different in either arm (Fig 5). The meeting where these data

were first presented included presentations from other cancer

study groups: the acute leukaemia cooperative group B; the

Southwest cancer chemotherapy study group; the Veterans

Administration hospitals and the Midwest cooperative group.

Fig 4. Sequential and combination therapy of acute leukaemia in a child with acute leukaemia. From: Burchenal, J.H., Ellison, R.R., Murphy, M.L.,

Karnofsky, D.A., Sykes, M.P., Tan, T.C., Mermann, A.C., Yuceoglu, M, Myers, W.P., Krakoff, I. & Alberstadt, N. (1954a) Clinical studies on 6-

mercaptopurine. Annals of the New York Academy of Sciences, 60, 359–368,

Fig 5. Analysis of the results of treatment of 125 patients on two drug

programmes. The shaded area gives the number of complete remission

marrows seen in each group. This research was originally published in

Blood. Heyn, R.M., Brubaker, C.A., Burchenal, J.H., Cramblett, H.G. &

Wolff, J.A. (1960) The comparison of 6-mercaptopurine with the

combination of 6-mercaptopurine and azaserine in the treatment of

acute leukaemia in children: results of a cooperative study. Blood, 15,

350–359. � the American Society of Hematology.

Historical review


These eventually developed into the Children’s Cancer Study

Group, of which Burchenal was one of the founding fathers,

allowing a coordinated approach to studies in childhood

leukaemia.

A British haematologist, Professor Frank Hayhoe, was

staying with Burchenal at his home in Connecticut prior to

attending a meeting at the Henry Ford Hospital, Detroit in

1956 when news of the use of the combination of 6MP and

azaserine broke. This was before the final results of the trial

were published. On arrival at the conference in Detroit, copies

of that day’s New York Times were on the table. There was a

huge, double-page spread with the chemical formulae for the

de novo synthesis of the nucleic acids and the intermediate

compounds under the heading ‘The one-two for leukaemia’.

The ‘one-two’ referred to 6MP and azaserine and the knockout

effect they would have on the disease, although the clinicians

present wondered wryly whether any of the population of New

York would be able to follow the chemical sequence (Christie

& Tansey, 2003). The two-drug combination did not live up to

its early promise and azaserine subsequently disappeared from

trials. However, the idea of combination therapy did not

disappear and this trial paved the way for Burchenal and other

researchers to continue with combinations of the increasing

number of drugs being shown to have activity against

leukaemia. These included cyclophosphamide and vincristine

in the late 1950s (Fernbach et al, 1960; Tan et al, 1961;

Johnson et al, 1963) and asparaginase in the 1960s (Hill et al,

1967). Tan’s and Burchenal’s paper on cyclophosphamide in

children with acute leukaemia was the last of 55 abstracts

presented at the 4th Annual Meeting of the American Society

of Hematology, held at the Ambassador Hotel in Los Angeles,

California, but was listed as only ‘To be read if time permits’.

As well as the need to achieve remission in the bone marrow,

it became apparent as children survived longer, that leukaemia

could occur in ‘sanctuary sites’. Burchenal had noted that with

prolonged remission, some children developed ovarian or

testicular lymphosarcomas and that local surgery or irradiation

was usually enough to cure them (Burchenal, 1964). Addi-

tionally, Dr Don Pinkel from St Jude’s Children’s Hospital in

Memphis, Tennessee had noticed that the longer children

stayed in remission, the more likely they were to relapse in the

central nervous system (CNS). It had already been shown that

methotrexate could be given intrathecally and that this would

temporarily control meningeal leukaemia (Whiteside et al,

1958) and George and Pinkel (1965) had shown ‘prophylactic’

craniospinal irradiation plus intrathecal methotrexate was

much more successful at preventing CNS disease than trying to

treat overt CNS disease. Using a combination of vincristine

and prednisone in an induction phase, 6MP and methotrexate

in a ‘maintenance phase’ and CNS irradiation, Don Pinkel

introduced his ‘Total Therapy’ series of treatment regimens for

leukaemia, which resulted in a tremendous increase in the

survival rates of children with acute lymphocytic leukaemia

(George et al, 1968). Freireich and his team at the National

Cancer Institute were also using combination chemotherapy.

The regimen he used was named ‘VAMP’ and here for the first

time intensive, intermittent combination chemotherapy was

used with four drugs with differing modes of action: vincr-

istine, aminopterin, mercaptopurine and prednisone (Freireich

et al, 1964). This influenced the design of the successful MOPP

[mechlorethamine, vincristine (Oncovin), procarbazine, pred-

nisone] protocol for the treatment of disseminated Hodgkin

disease (DeVita & Serpick, 1967). The predicted 5-year survival

in children with acute lymphoblastic leukaemia was now 50%.

On 10 November 1964, Burchenal was invited to give the

2nd Annual Guest Lecture of the Leukaemia Research Fund,

which had been founded in 1960 by Dr Gordon Pillar

(Burchenal, 1964). The lecture was intended to help the

dissemination of knowledge of leukaemia and related disorders

and its contribution to medical science. In the lecture,

Burchenal outlined three basic approaches to research into

this disease. The first was the fundamental approach, where

qualitative differences between the leukaemic cells and normal

cells, such as specific nutritional requirements or enzyme

content, were sought, therefore allowing specific drugs to be

designed for selective killing. It was acknowledged that these

qualitative differences had not yet been found, although there

was mounting experience with anti-metabolites that were

designed on the same principle. The second was the empirical

approach, where new agents were screened against models of

leukaemia, such as rodent leukaemias, and their use in humans

was based on or guided by the results of such observation and

experiment but without any scientific knowledge as to why the

compounds should work. Although less intellectually satisfy-

ing, most chemotherapeutic agents against infectious disease

were developed in that way. The model used was that of

transplantable leukaemia in mice. If survival time increased,

then the drug was tested on a range of rodent leukaemias since

the broader the spectrum of animals responding, the more

likely the drug was to work in man. An extension of this work

was then to develop strains of leukaemia that were resistant to

one or other of the standard agents, which at that time were

methotrexate and 6MP. If the trial agent resulted in regression

of the leukaemia, it implied a different mechanism of action

and thus might be helpful in patients with resistant disease.

The third approach was the use of pharmacological and

biological studies. In these studies, compounds within a class

were compared for efficacy and toxicity, looking at the ratio of

the maximum tolerated dose to the minimal effective dose, the

chemotherapeutic index. Candidate drugs with the highest

therapeutic index were given preference in trials. He outlined

how 50% survival from diagnosis had increased from

2Æ5 months with the nitrogen mustards, to 5 months with

the anti-folates, to 7 months with 6MP and steroids and now

to 13 months with addition of cyclophosphamide and vincris-

tine. Strategies were being developed to prevent resistance,

which included cyclical therapy where the second or third

drugs were given after a predetermined time, either 6 weeks or

3 months, even if resistance had not yet developed to the first

drug (Brubaker et al, 1963; Zuelzer, 1963). He noted that this

Historical review


produced improved 5-year survival times but that the studies

were not randomised, and recommended such studies by

cooperative groups to confirm the potentially important

advance. With the increasing use of different drugs sequentially

and in combination, there were now rare, long-term survivors.

Burchenal felt that these patients must differ from ‘ordinary’

patients with leukaemia and had set up an Acute Leukaemia

Taskforce to conduct a worldwide survey to identify such

patients. This idea had grown from a meeting of the five cancer

study groups in America investigating acute leukaemia, which

he chaired in 1959 (Burchenal, 1960). Preliminary results

showed that of 53 clinics contacted, 103 patients had been

identified who had survived more than 5 years; all had been

treated with steroids, 6MP, azaserine, methotrexate or com-

binations of these. Of 82 children, 58 were alive and disease-

free 5–14 years from diagnosis and of 21 adults, eight were

disease-free 5–9 years from diagnosis. Of the patients who

were still alive at 5 years but not disease-free, none survived for

more than 8 years and no patient had died once they had been

in remission for more than 8 years. He concluded his lecture

by stating his opinion, that the best chance for control was a

multi-disciplinary attack on the disease, which involved

chemotherapy, irradiation and occasional surgery for the few

children who developed ovarian or testicular lymphosarcomas

after prolonged remission. He recognised that new and better

chemotherapeutic agents were necessary and that they must be

studied to determine optimal therapeutic doses and schedules

and in combinations that would enhance therapeutic effect and

diminish toxicity. Professor David Galton gave the vote of

thanks.

Burchenal divided the history of cancer chemotherapy into

five phases: the realisation that chemotherapy of cancer might

be possible; the discovery and evaluation of new anti-tumour

agents; the development of sanctuary therapy with intrathecal

methotrexate or craniospinal irradiation or both; development

of intensive combination chemotherapy and the development

of combined modality (adjuvant) therapy (Burchenal, 1977).

Treatment of some lymphomas, such Burkitt lymphoma and

Hodgkin lymphoma, and of certain tumours, including

choriocarcinoma and testicular tumours, was successful with

chemotherapy alone and Burchenal had recognised that

Burkitt lymphoma could be used as a model or ‘stalking

horse’ for the treatment of leukaemia (Burchenal, 1966).

However, results in other tumours, such as carcinoma of the

lung, breast and colon, were not good. Burchenal advocated

the use of multimodal or adjuvant therapy for these poorly

responsive cancers. The rationale for multimodal therapy,

utilising surgery, radiation, chemotherapy and immunothera-

py, came from the observation that initial localised therapy,

removing the bulk of visible tumour surgically with irradiation

to the tumour bed, and then treating metastases when they

arose with radiation and chemotherapy was not producing the

cures that had been hoped for. It became apparent that,

although the disease appeared localised, there must be occult

micrometastases already present that were left untreated to

enlarge and result in distant relapse. The chemotherapy of

most advanced metastatic tumours was not successful, at best

being palliative, at worst toxic and ineffective. Surgery and

radiotherapy are limited, not by the size of the tumour, but by

its extension, whereas chemotherapy and immunotherapy are

limited not by the extension of the tumour but by its total

mass. The plan was to give adjuvant therapy as soon as possible

after surgery in order to destroy the vulnerable micrometa-

stases before they become macroscopic and relatively insensit-

ive. Certain children’s tumours were particularly amenable to

this approach, one such being Wilms tumour. The cure rate

rose to 80% using surgery, radiotherapy and chemotherapy

with actinomycin D almost simultaneously and then for a

further 3 months (Farber, 1966), whereas previously it had

been around 20% (Klapproth, 1959). Ewing sarcoma, embry-

onal rhabdomyosarcoma and osteogenic sarcoma also showed

significant improvement in cure rates with this approach.

Improvements were also being seen in adults, particularly in

women with breast cancer.

Trials of new chemotherapeutic agents and adjuvant ther-

apies in children and adults with leukaemia and cancer

required courage and trust on the part of the patients and

parents and courage and compassion on the part of the doctor.

Success was not guaranteed, the treatments were difficult and

debilitating and in the early days, many medical and nursing

staff felt that it was unethical to treat children with leukaemia

as such treatment was futile and would only prolong their

distress. Fortunately, there were pioneers, such as Burchenal,

who had the vision, the energy and the colleagues to take up

the challenge of treating cancer and to move the goal from

palliation to cure. He spent his last years in New Hampshire

with his wife and was keenly interested in developments in

this field up until his death on 8 March 2006. In 1996, the

American Association for Cancer Research of which Burchenal

was a past president, established an annual lecture in his name

for outstanding achievements in clinical cancer research.

Acknowledgements

I would like to thank Iain Milne and Estela Dukan from the

library of the Royal College of Physicians, Edinburgh for their

help with the references, and Marissa Green from Public

Affairs at Memorial Sloan-Kettering for the archive photo-

graphs of Joe Burchenal. Much of the personal information

about Joe Burchenal’s early career is from a book by John

Laszlo, which is cited in the references, and also from

discussion with Joe and Joan Burchenal.

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Joe Burchenal and the birth of combination chemotherapy

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