WHAT IS CANCER AND HOW DOES IT AFFECTTHE HUMAN CONDITION ?

Karobi Karobi Moitra (Ph.D)Moitra (Ph.D)NCI Frederick , NIHNCI Frederick , NIHCancer Inflammation ProgramCancer Inflammation ProgramHuman Genetics SectionHuman Genetics SectionFrederick MD.Frederick MD.

Is cancer a single disease

or

a group of diseases ?

Cancer is a group of related diseases which arecharacterized by uncontrolled cellular growth

and division

Cancer is associated with abnormal cellularproliferation

Cells divide when they should not divide and theylack the normal control systems to shut off unwanted

cell division

a

R

Loss of Normal Growth Control

Cancer cell division

Fourth orlater mutation

Thirdmutation

Secondmutation

Firstmutation

Uncontrolled growth

Cell Suicide or Apoptosis

Cell damage—no repair

Normal cell division

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R

In most cases to form a contiguous cell masscalled a tumor

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Example of Normal Growth

Cell migration

Dermis

Dividing cellsin basal layer

Dead cellsshed from

outer surface

Epidermis

Each time one of these basal cells divides, it produces two cells. One remains in the basal layer andretains the capacity to divide. The other migrates out of the basal layer and loses the capacity todivide. The number of dividing cells in the basal layer, therefore, stays the same.

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The Beginning of Cancerous Growth

During the development of skin cancer, the normal balance between cell division and cell loss is disrupted.The basal cells now divide faster than is needed to replenish the cells being shed from the surface of theskin. Each time one of these basal cells divides, the two newly formed cells will often retain the capacity todivide, thereby leading to an increase in the total number of dividing cells.

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Cell death =Cell growth

Cell death <Cell growth

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Tumors (Neoplasms)

Underlying tissue

This gradual increase in the number of dividing cells creates a growing mass of tissue called a “tumor” or “neoplasm.”

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Melanoma

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Types of cancer / precancerous subtypes:

According to growth type:

Neoplasia - growth of cells to form a new structure eg: a tumor

Hyperplasia - excessive no. of cells.

Dysplasia - loss of normal arrangement of tissue (precancerous)

Carcinoma-in-situ - uncontrolled growth of cells that remains at the same place (non-invasive).

Invasive carcinoma - can invade surrounding tissue and also undergo metastasis.

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R

Normal to Invasive

Milddysplasia

Carcinoma insitu (severedysplasia) Cancer

(invasive)

Normal Hyperplasia

Excessive growth Loss of cellular structure& tissue arrangement

Excessive growth in place

Invades

a

R

According to tissue type affected :

Carcinoma - tumors made up of principally epithelial cells (cells that line inner and outer surfaces). eg: cervical and skin cancers.

Sarcoma - made up principally of connective tissue cells (cartilage, bone etc.) eg: osteosarcoma.

Leukemia - Neoplastic growth of leucocytes (WBC) .

Lymphoma - excessive production of lymphocytes by lymph nodes and spleen. eg: Hodgkins disease.

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According to metastasis (invading capacity)

Benign tumor - these tumors have restricted growth and tend to remain localized. eg: wart.

Malignant tumor - these tumors do not remain localized but invade other tissue and give rise to secondary tumors in other parts of the body (metastasis).

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Malignant versus Benign Tumors

Malignant (cancer)cells invadeneighboring tissues,enter blood vessels,and metastasize todifferent sites

Time

Benign (not cancer)tumor cells growonly locally and cannotspread by invasion ormetastasis

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Invasion and Metastasis

3Cancer cellsreinvade and growat new location

1Cancer cells invadesurrounding tissuesand blood vessels

2Cancer cells aretransported by thecirculatory systemto distant sites

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R

According to tissue type affected :

Carcinoma - tumors made up of principally epithelial cells (cells that line inner and outer surfaces). eg: cervical and skin cancers.

Sarcoma - made up principally of connective tissue cells (cartilage, bone etc.) eg: osteosarcoma.

According to growth type:

Neoplasia - growth of cells to form a new structure eg: a tumor

Hyperplasia - excessive no. of cells.

Dysplasia - loss of normal arrangement of tissue (precancerous)

Carcinoma-in-situ - uncontrolled growth of cells that remains at the same place (non-invasive).

Invasive carcinoma - can invade surrounding tissue and also undergo metastasis.

Leukemia - Neoplastic growth of leucocytes (WBC) .

Lymphoma - excessive production of lymphocytes by lymph nodes and spleen. eg: Hodgkins disease.

According to metastasis (invading capacity)

Benign tumor - these tumors have restricted growth and tend to remain localized. eg: wart.

Malignant tumor - these tumors do not remain localized but invade other tissue and give rise to secondary tumors in other parts of the body (metastasis).

Different kinds of cancer

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Microscopic Appearance of Cancer Cells

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Cancer cell Normal cell

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Characteristic adaptive features of cancer cells :

1. Loss of contact inhibition

Normal cells stop growing when their plasma membranescome into contact with one another - normal cells stop moving when they contact each other this is called contact inhibition, cancer cells lose the property of contact inhibition. Transformed cells do not stop dividingafter forming a monolayer division continues until severallayers of cells are formed.

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2. Unrestrained control of growth

Cancer cells lack the normal control systems to shutoff unwanted growth.

3. Metastasis

Metastasis is the spread of cancer cells from a primarysite of origin to other tissues where they grow as secondary tumors.

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Some biochemical properties of cancer cells :

1. Increased glycolysis (Warburg effect)Otto Warburg observed that virtually every type of cancercells that form solid tumors excrete much larger quantities oflactic acid than its normal counterpart. This is known as the‘Warburg effect’.Unlike normal cells, which break down sugar using oxidativepathways (or the Krebs cycle), tumor cells used non-oxidative pathways (glycolysis) to generate energy fromsugar.

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2. Alterations in cytoskeletal proteins

Less organized/ disorganized arrangement of cytoskeletal proteins - such as myosin , tubulin etc.

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3. Loss of anchorage dependence

Cancer cells in culture can grow suspended in media while most normal cells need to attach to a substratum to grow (anchored).

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4. Cancer cells are seemingly immortal

Cancer cells in culture can continue to grow indefinitely.

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The Somatic Mutation TheoryOf Cancer

Theodore Boveri 1914

He stated that the fundamentalcause of cancer was in chromatinimbalance in the cells from which cancer arises.

Evidence : Many cancers havechromosomal abnormalities

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What Causes Cancer?

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What Causes Cancer?Some viruses or bacteria

HeredityDiet

Hormones

RadiationSome chemicals

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Tobacco Use and CancerSome Cancer-Causing Chemicals in Tobacco Smoke

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Low-Strength Radiation

Annual Sunshine(UV radiation)

SkinCancer

Incidence

Most

Dallas

Pittsburgh

High

Detroit

LowLeast

Some atoms give off radiation, which is energy that travels through space. Prolonged or repeatedexposure to certain types of radiation can cause cancer. Cancer caused by the sun’s ultravioletradiation is most common in people who spend long hours in strong sunlight. Ultraviolet radiationfrom sunlight is a low-strength type of radiation. Effective ways to protect against ultraviolet radiationand to prevent skin cancer are to avoid going into strong, direct sunlight and to wear protectiveclothing. Sunscreen lotions reduce the risk of some forms of skin cancers.

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High-Strength Radiation

Most

High

LowLeast

LeukemiaIncidence

X-ray Dose(atomic radiation)

Increased rates of cancer also have been detected in people exposed to high-strength forms of radiation such asX-rays or radiation emitted from unstable atoms called radioisotopes. Because these two types of radiation arestronger than ultraviolet radiation, they can penetrate through clothing and skin into the body. Therefore, high-strength radiation can cause cancers of internal body tissues. Examples include cancer caused by nuclear falloutfrom atomic explosions and cancers caused by excessive exposure to radioactive chemicals.

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Viruses

Virus insertsand changesgenes forcell growth

Cancer-linked virus

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Examples of Human Cancer Viruses

Some Viruses Associated with Human Cancers

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Bacteria and Stomach Cancer

H. pyloriPatient’stissue

sample

The bacterium Helicobacter pylori, which can cause stomach ulcers, has been associated with thedevelopment of cancer, so people infected with H. pylori are at increased risk for stomach cancer.Research is under way to define the genetic interactions between this infectious agent and its hosttissues that may explain why cancer develops.

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Heredity and Cancer

Inherited factor(s)

All Breast Cancer Patients

Other factor(s)

Cancer is not considered an inherited illness because most cases of cancer, perhaps 80 to 90 percent, occur in peoplewith no family history of the disease. However, a person’s chances of developing cancer can be influenced by theinheritance of certain kinds of genetic alterations. These alterations tend to increase an individual’s susceptibility todeveloping cancer in the future. For example, about 5 percent of breast cancers are thought to be due to inheritance ofparticular form(s) of a “breast cancer susceptibility gene.”

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Cancer is a group of related diseases which arecharacterized by uncontrolled cellular growth

and division

Cells divide when they should not divide and theylack the normal control systems to shut off unwanted

cell division

CANCER

----------------------

"He who cures a disease maybe the skill fullest, but he that

prevents it is the safestphysician”

Thomas Fuller

Adapted from The Biology ofCancer

First Edition

Chapter 3, 4 & 7

Copyright © Garland Science 2007

Robert A. Weinberg

Karobi Moitra (Ph.D)Karobi Moitra (Ph.D)NCI Frederick , NIHNCI Frederick , NIHCancer Inflammation ProgramCancer Inflammation ProgramHuman Genetics SectionHuman Genetics SectionFrederick MDFrederick MD..

Tumor VirusesOncogenes &Tumor Supressor genes

Figure 3.1 The Biology of Cancer (© Garland Science 2007)

Peyton Rous and Rous Sarcoma Virus (RSV)

1910 1966

Figure 3.4a The Biology of Cancer (© Garland Science 2007)

The Virion (virus particle) of RSV and other related viruses:RNA viruses (retroviruses) can cause cancer

Figure 3.19 The Biology of Cancer (© Garland Science 2007)

Structure of the RSV genome

ALV = Avian leukosis virus Oncogene

Figure 3.7a The Biology of Cancer (© Garland Science 2007)

Normal cells can be converted into tumor cells (transformation)

Table 3.1 The Biology of Cancer (© Garland Science 2007)

Oncogenes &Proto-oncogenes

Genes and Cancer

Chromosomesare DNAmolecules

Heredity

RadiationChemicals

Viruses

Chemicals (e.g., from smoking), radiation, viruses, andheredity all contribute to the development of cancer by

triggering changes in a cell’s genes

Normal cellular genes with the potential to become oncogenesare called proto-oncogenes

Oncogenes or tumor genes are genes with potential properties for theinduction of neoplastic transformation

(either in natural or experimental conditions)

(Duesberg 1980)

Proto-oncogene Oncogene

Receptor

Normal Growth-Control Pathway

DNA

Cell proliferation

Cell nucleus

Transcriptionfactors

Signaling enzymes

Growth factor

Proto-Oncogenes and Normal Cell Growth

Oncogenes are related to normal genes called proto-oncogenes that encode components of the cell’s normalgrowth-control pathway. Some of these components are growth factors, receptors, signaling enzymes, andtranscription factors. Growth factors bind to receptors on the cell surface, which activate signaling enzymesinside the cell that, in turn, activate special proteins called transcription factors inside the cell’s nucleus. Theactivated transcription factors “turn on” the genes required for cell growth and proliferation.

Mutated/damaged oncogene

Oncogenes accelerate cell growth and division

Cancer cell

Normal cell Normal genes regulate cell growth

Oncogenes are genes whose PRESENCE incertain forms and/or overactivity canstimulate the development of cancer.

Oncogenes or tumor genes are genes with potential properties for theinduction of neoplastic transformation

(either in natural or experimental conditions)

(Duesberg 1980)

The word oncogene comes from the word ‘onkos ‘ meaning tumor

When a proto-oncogene becomes activated it iscalled an oncogene

Proto-oncogene Oncogene

When an oncogene becomes activated it mightcause cancer

Proto-oncogene -> oncogene -> other steps -> cancer

Activation of Oncogenes

1. Mutation

a. Insertional mutagenesis

b. Point mutagenesis

2. Amplification

3. Translocation

Mutation : A mutation is a permanent change inthe DNA sequence of a gene. Mutations in agene's DNA sequence can alter the amino acidsequence of the protein encoded by the gene.

Figure 3.23b The Biology of Cancer (© Garland Science 2007)

ALV provirus may become integrated with the c-myc oncogene

ALV switches on c-myc

1a. Insertional Mutagenesis

1b. Mutagenesis of oncogenes

Altered polypeptides produced by mutant oncogenes could berelated to the origin of some human tumors

Activation of oncogenes

Figure 4.10 The Biology of Cancer (© Garland Science 2007)

Mutation responsible for H-ras oncogene activtion

Human bladder cancer oncogene - 12th codon of H-ras ,mutation converts glycine codon to valine codon

Activation of oncogenes

2. Amplification of oncogenes

Activation of oncogenes

More than one copy of a gene:Amplification

How are oncogenes amplified?

Double minute chromosomes

Activation of oncogenes

3. Translocation

A karyotype is the number and appearanceof chromosomes in the nucleus of a

eukaryote cell

A chromosome translocation is a chromosomeabnormality caused by rearrangement of partsbetween nonhomologous chromosomes. A genefusion may be created when the translocationjoins two otherwise separated genes, theoccurrence of which is common in cancer.

Figure 4.13a The Biology of Cancer (© Garland Science 2007)

Burkitts lymphoma t(8;14) the c-myc gene is placed under the control of the enhancer sequence of an immunoglubulin gene

Tumor Suppressor Genes

Tumor Suppressor Genes

Tumor suppressor genes are normal genes whose ABSENCE can lead to cancer

i.e. Tumor suppressor genes protect the cell

Tumor Suppressor Genes - Tumor suppressor genes are normal genes whose ABSENCE can lead to cancer

i.e. Tumor suppressor genes protect the cell

Normal genes prevent cancer

Remove or inactivatetumor suppressor genes

Mutated/inactivatedtumor suppressor genes

Damage to both genes leads to cancer

Cancer cell

Normal cell

If a pair of tumor suppressor genes are eitherlost from a cell or inactivated by mutation,their functional absence might allow cancerto develop

Tumor Suppressor GenesAct Like a Brake Pedal

Tumor SuppressorGene Proteins

DNACell nucleus

Signalingenzymes

Growth factor

Receptor

Transcriptionfactors

Cell proliferation

Tumor suppressor genes are a family of normal genes that instruct cells to produce proteins that restrain cell growth and division. Since tumorsuppressor genes code for proteins that slow down cell growth and division, the loss of such proteins allows a cell to grow and divide in anuncontrolled fashion. Tumor suppressor genes are like the brake pedal of an automobile. The loss of a tumor suppressor gene function is likehaving a brake pedal that does not function properly, thereby allowing the cell to grow and divide continually.

Tumor suppressors act similar to the ‘brakes’ of a car (analogy)

p53 Tumor Suppressor ProteinTriggers Cell Suicide

Normal cell Cell suicide(Apoptosis)

p53 protein

Excessive DNA damage

One particular tumor suppressor gene codes for a protein called “p53” that can trigger cell suicide (apoptosis). In cellsthat have undergone DNA damage, the p53 protein acts like a brake pedal to halt cell growth and division. If the damagecannot be repaired, the p53 protein eventually initiates cell suicide, thereby preventing the genetically damaged cellfrom growing out of control.

pRB - Tumor suppressor gene

From R Bernards

Chapter 11:Multi-Step Tumorigenesis

Copyright © Garland Science 2007

The Multistep Nature of Cancer

Karobi Moitra (Ph.D)Karobi Moitra (Ph.D)NCI Frederick , NIHNCI Frederick , NIHCancer Inflammation ProgramCancer Inflammation ProgramHuman Genetics SectionHuman Genetics SectionFrederick MD.Frederick MD.

Clonal Expansion in Cancer

Peter Nowell (1976) hypothesized the clonal evolution of tumorswhere a tumor arises initially from 1 specific cell which then developsa growth advantage over other cells.

Multistep Genetic damage leads to Cancer

Normal cells evolve into cells with increasinglyneoplastic phenotypes through a process called

Tumor Progression

Normal to Invasive

Milddysplasia

Carcinoma insitu (severedysplasia) Cancer

(invasive)

Normal Hyperplasia

Excessive growth Loss of cellular structure& tissue arrangement

Excessive growth in place

Invades

Figure 11.7 The Biology of Cancer (© Garland Science 2007)

Carcinoma-in -situ

PIN = prostate intraepithelial neoplasiaCIN = cervical intraepithelial neoplasiaLeukoplakia = white patches of keratin(precancerous).Adenoma = tumor of glandular origin

Figure 11.10 The Biology of Cancer (© Garland Science 2007)

Genetic changes in Multistep TumorigenesisAdenomatous Polyposis Coli (Colon cancer)

Note: DNA hypomethylation means undermethylation, it’s role in canceris not clearly understood.

18q TSG = DCC- deleted in colorectal cancer

The process of tumor formation is complex and involvesmultiple steps

The complexity of this process is reflected in the longtime periods required for most human cancers to develop

These changes involve both the activation of oncogenesand the inactivation of tumor suppressor genes

Chapter 8:pRb and Control of the

Cell Cycle Clock

Copyright © Garland Science 2007

Karobi Karobi Moitra (Ph.D)Moitra (Ph.D)NCI Frederick , NIHNCI Frederick , NIHCancer Inflammation ProgramCancer Inflammation ProgramHuman Genetics SectionHuman Genetics SectionFrederick MD.Frederick MD.

The Cell Cycle

The cell cycle is a programmedseries of events that enablesa cell to duplicate its contentsand generate 2 daughter cells

Figure 8.3b The Biology of Cancer (© Garland Science 2007)

The Cell Cycle

Resting stage

Gap 1Synthesis

Gap2

Figure 8.3a The Biology of Cancer (© Garland Science 2007)

The mitotic cell cycle in newt lung cells

Prophase:ChromosomesCondense (blue)

Prophase:Centrosomesbegin to assemble(green)

Metaphase:Chromosomesalign and attachto spindle fibres

Anaphase:Chromosomehalves are pulled apart

Telophase:Chromatidsdecondenseand nuclearmembraneforms

Checkpoint Control

Checkpoint Control

Checkpoint controls in the cell cycle ensure thata new step in the cycle is not undertaken until

the preceding step has been completed.

Figure 8.4 The Biology of Cancer (© Garland Science 2007)

Cell Cycle Checkpoints : Quality Control

What happens if a damaged cell overrides these checkpoints?

Cancer is associated with abnormal cellularproliferation

Cells divide when they should not divide and theylack the normal control systems to shut off unwanted

cell division

Cancer Cells May Lose Checkpoint Controls

Cell death

Figure 8.6 The Biology of Cancer (© Garland Science 2007)

Once a Cell Advances beyond R- restriction point it is committed to advance through the cell cycle and

divide

Go to MRemain in G1Go to G0

Restriction Point :

G1 phase checkpoint in the cell cycle of animal cells

Figure 8.1 The Biology of Cancer (© Garland Science 2007)

The Cell Cycle Clock controls the cell cycle

Figure 8.8 The Biology of Cancer (© Garland Science 2007)

Each cyclin pairs with a specific cyclin dependentkinase (CDK) to carry out the steps in the cell cycle

Figure 8.12 The Biology of Cancer (© Garland Science 2007)

Coordinated cyclin levels during the cellcycle : levels of different cyclins change

at different stages in the cell cycle

Figure 8.13a The Biology of Cancer (© Garland Science 2007)

p - designation of a tumor suppressor gene

CDK inhibitors block the action of CDK’s at various pointsin the cell cycle

Preventsdamaged cells

to proceed withthe cell cycle and also

causes interchange of CDKsat different stages of the

cell cycle

pRB and cell cycle control

The E2F transcription factor

E2F is a transcription factor which can switch on genesthat can cause cell division. Rb can inactivate E2F.

Mutations inactivate pRb, p16 (TSG’s) & the abnormal cell replicates

How can knowledge of the cell cycle can be utilized to develop anticancer drugs?

The cell cycle is a programmed series of events that enables a cell to duplicate its contents

and generate 2 daughter cells

Checkpoint controls in the cell cycle ensure thata new step in the cycle is not undertaken until

the preceding step has been completed.

Many types of cancer cells have inactivatedone or more of these checkpoint controls to propel

neoplastic growth.

The Hallmarks of Cancer

Karobi Karobi Moitra (Ph.D)Moitra (Ph.D)NCI Frederick , NIHNCI Frederick , NIHCancer Inflammation ProgramCancer Inflammation ProgramHuman Genetics SectionHuman Genetics SectionFrederick MD.Frederick MD.

Acquired Capabilities of Cancer

Cells

1. Self-Sufficiency in growth signals

Normal cells require mitogenic (cell div) growth signals to move from a quiescent (resting) state into an active proliferation state. Cancer cells can generate their owngrowth signals.

Autocrine signaling : Secretion of a substance or growthfactor that acts on a cell that produced it (i.e. IL2 signaling in monocytes )

Paracrine signaling: secretion of a substance or growth factor that acts on a nearby cell (i.e. neurotransmitter signaling)

Autocrine

How do cancer cells generate their own growth signals ?

Autocrine signaling: a cancer cell can manufacture it’sown autocrine growth factors.

Active transforming growth factor beta blocks proliferation in normal cell, while downregulation of TGF-betain a cancer cell can induce proliferation by upregulation of cyclins and autocrine growth factors(hypothetical example Grimm and Rosen 2006).

Cancer cells can also switch the types of Extracellular matrix receptors (ECM) they express favoring the

ones that transmit growth signals

ECM : extracellular part of tissue that provides structuralsupport to the cells and performs various other functions

Activation of the Ras-raf pathway through integrins(integrins can mediate signals from the ECM to thecell)

Growth signals

MEK - mitogen activatedprotein kinase kinase

ERK -Extracellular signal regulated kinase

GRB2- growth factor receptor bound protein

2. Insensitivity to Antigrowth signals

If cancer cells are to survive they must block anti-growthsignals. Antigrowth signals can block proliferation by a. Forcing a cell out of the cell cycle into G0.b. Inducing a cell to enter post-mitotic differentiated state.

E2F is a transcription factor which can switch on genesthat can cause cell division. Rb can inactivate E2F.

3. Evading Apoptosis (cell suicide)

Mutations in p53 can derail apoptosis (preventcell suicide)

What happens when there is a ‘mistake’ or mutation in the code?

Insulin like Growth Factors (IGFs) trigger pro-survival(anti-apoptotic) pathways

4. Limitless Replicative Potential

Normal cells age by shortening of chromosomes whentheir telomeres degrade

Telomere

Telomerase synthesizes and maintains telomeresin cancer cells

5. Sustained Angiogenesis

Angiogenesis is the growth of new blood vessels

6. Tissue invasion and metastasis

Cancer cells synthesize collagenase type lV

E- Cadherin

E-cadherin is disregulated in invasion and metastasis

Loss of anchorage dependence

Reference: The Hallmarks of Cancer , Hanahan D and Weinberg R (2000) Cell, 100: 57-70.

Cancer is associated with abnormal cellularproliferation

Cells divide when they should not divide and theylack the normal control systems to shut off unwanted

cell division