Community Cancer ClustersMonica Brown, PhDCancer Epidemiologist, the California Cancer Registry

CANCER BIOLOGY (BIO-183), DR. HAO NGUYENFEBRUARY 21, 2011SACRAMENTO STATE UNIVERSITY, DEPT OF BIOLOGICAL SCIENCES

What Drives the Public’s Concern of the Clustering of Cancers in Communities & Workplaces?

• There is considerable public concern that environmental exposures cause an excess in cancers in some communities.

• The public believes environmental pollutants/toxins increase risk of cancer – although.

• Cancer clusters may be suspected when people notice that several family members, friends, neighbors or co-workers have been diagnosed with cancer.– Although the distribution of cancers may be “normal” given

the age, sex, race/ethnic and lifestyle of that group.

… continued• Other phenomena that may drive suspicion

of environmental cancer clusters are...– Media reports sensationalized cancer clusters– Distrust of government, manufacturing &

business– Fear that we’ve created an environment filled

with hazards that is causes us & our families harm

– The perceived inability to control cancer risk & environmental hazards

– Ever changing & varied Public Health (PH) messages

What We know

• Cancers are common! 1 in 5 Californians will have a cancer in their lifetime

• Cancers are complex diseases! Cancer is a general term for many diseases – most with different etiologies; many of which are unknown

• Cancer incidence varies predictably by age, sex, race/ethnicity & risk factors.

• Community members can be similar in age, SES, race/ethnicity & lifestyles – these factors contribute more to cancer incidence than shared environment

What We know, continued

• There’s no evidence that carcinogens in amounts typically present in the air, soil or drinking water increases the risk of developing cancer in the general population

• Exposure to a carcinogen and the onset of cancer is not certain, other factors, some known, may be required. When cancer does develop, the onset can be decades from exposure.

• Knowledge of cancer causes, its distribution and prevention varies greatly in the general public – – PH has done a poor job educating the public about

cancer; therefore the public has many misconceptions about cancer & cancer clusters

Causes of Cancer

Lifestyle68%

Environment/Occupation

19%

Family History/Genetics

13%

Lifestyle•Tobacco Use 30%•Diet 10%•Physical Inactivity 5%•Alcohol Use 3%•Other 20%

Environmental/Occupation•Occupation 5%•Viruses/other biologics 5%•SES 3%•Pollution 2%•Radiation 2%•Other 2%

Family History/Genetics•Family History 5%•Prenatal Factors/Growth 5%•Reproductive Factors 3%

Source: Harvard Report on Cancer Prevention, 1996

Common Misconceptions about Cancer Clusters

Clustering is uncommon

Clustering of health events is common - some random (1%) some not. Shared social-demographic characteristics and/or similar lifestyles explains some health event clustering.

Several cancer cases make a single cause cluster

We expect a certain number & certain types of cancers in every neighborhood/workplace.

If there are several cases of cancers in a community, of different types, they must come from the same source.

If there are several different types of cancers in a community, there are likely several different causes.

Examples of Documented Cancer Clusters

Cluster Characteristic AgentRare

Incr dz freqAngiosarcoma of the liver among factory workers Rare

Vinyl Chloride

Mesothelioma among Native American silversmiths Rare asbestos

Incr dz frequnique pop

Diethyl-stilbestrol

Adenocarcinoma of vagina among young women

Kaposis sarcoma among young men HIV

CANCER CLUSTERS IN CALIFORNIA

The California Cancer Registry

• The California Cancer Registry (CCR) is administered by the California Department of Public Health (CDPH).

• The CCR is a true population-based registry.– Cancer reporting is mandated for hospitals & physicians.– Every case diagnosed among residents reported since 1988

• Data collected by the registry are used:– To monitor incidence & mortality.– For research into the causes, cures & prevention of cancer; – To produce reports including the state & regional reports;

the American Cancer Society’s Cancer Facts & Figures– The evaluation of community cancer concerns.

The CCR defines a Cancer Cluster as…

an aggregation of cancer cases that has been determined to be unusual when compared to the cancers that would be expected if the group of location in question had the same cancer rates as the underlying population.

The cluster must differ substantially from the expected pattern in number, type, or the age of cases.

When a Californian has a Cancer Concern: the Role of the CCR

• The CCR and it’s regional cancer registries respond to numerous requests for evaluation of community and workplace cancer concerns.

• The registry’s role is to statistically assess whether the number of cases of targeted cancers observed in a community or workplace are significantly greater than what would be expected.

• If there is a statistically significant excess of cases, report to the Environmental Health Investigations Branch (EHIB) of CDPH who will investigate.

The CCR does not …

• Conduct epidemiologic “outbreak”, clinical or laboratory investigations.

• On-site surveys of residents or employees to assess risk.

• Direct others in exposure assessments.• Coordinate the efforts of other state and

county agencies in their investigations.

CCR PROCEDURES FOR EVALUATION OF A REPORTED CANCER CLUSTER

Step One: Obtain Information from Informant

• Caller’s name & address; affiliation (community member)

• Number of specific cases observed

• Cancer type(s) observed• Age, sex, race/ethnicity of cases• Geographic area or group• Time period of concern• Method of observation – how

did the caller learn of the cases

Step Two: Provide Cancer Education & Information to Informant

• Education– The frequency of specified cancers in their

community or County– Risk factors for specified cancers– If knowledgably, discuss agent and/or

exposure

• Information– American Cancer Society (ACS)– Centers for Disease Control and Prevention

(CDC)– The National Institutes of Health (NIH)– Agency for Toxic Substances and Disease

Registry (ATSDR)

Note: Do not assume that everyone has access to or can use the internet

Indications for Statistical EvaluationOther Considerations• Are cancers unusual in number,

type or age of patients?• Has a potential carcinogenic agent

been identified?– If a specific exposure is suspected

– test 1st – call County Environmental Health, Environmental Protection Agency (EPA) or if workplace, Occupational Safety and Health Agency (OSHA)

• Is there a plausible exposure pathway?

• Is the request coming from a another State agency or from a County Health Department?

• Is informant representing a community or workplace action group?

• Are children involved?• Is this perceived cancer cluster

“political” or is it already being followed by the press?

Step Three: Determine if an Evaluation is Needed

+

occurrence in unique

population

increased cancer

frequency

unusual cancer

carcinogenic agent

biologic plausibility

cases documented in the

CCRFurther

Action is Warranted

Step Four: Explain Procedure, Limitations & Provide Timeline to Informant

• Procedure– We use registry data to confirm case information &

determine clinical characteristics of cancers– We use census data for denominators (population

at risk)– Perform calculations, write report to county & state.– In the event of a statistically significant excess of

cancers, we refer case to EHIB for investigation• Limitations

– CCR will not contain most recently diagnosed cases– Only a substantial increase in risk is likely to be

detected– We lack information on length of residence and risk

factors that may contribute to developing cancer• Timeline: 1-3 months

Workplace Cancer Concerns: Barriers to Evaluations

• Obtaining appropriate information on ill & well (population at risk) employees from employers is difficult to impossible.

• Sometimes we must obtain permission from employees to access their medical records.

• Assessing biologic plausibility: Does the suspected workplace agent associated with increased risk of the reported cancers?– Does workplace exposure have an impact?

• direct vs. indirect• length of exposure (workday/year(s))• mode of exposure (eat/drink, inhale etc.)

– What other risk factors could increase risk of developing reported cancers, that cannot be assessed?

• smoking, drinking & diet

• What cancers would be “normal” for this employee population – given age, sex, race/ethnicity & lifestyle– Are there behaviors that are common in this employee

group?

Step Five: Consult and Notify Relevant Officials of Report

• Management hierarchy of CDPH• County Health Officer• Workplace management

Step Six: Conduct Assessmentdefine

geographic area by census tract(s)

establish case definition (age, sex,

race/ethnicity; type of cancers)

confirm & review suspected cases

(numerator)

define population denominator in

person-years (time period)

generate expected number

of cases

compare cases observed to expected,

calculate 99% confidence interval

if observed cases are in excess, determine if statistically significant

Step Seven: Communicate Results • Report results of evaluation to the …

– Informant– County Health Officer– CSRB management hierarchy

• If results show a statistically significant excess in cases, include …– EHIB– CDPH public affairs office

CHALLENGES & CONCLUSIONS

Greatest Challenge: Communicating Results to the Public

• Science– Scientific evidence is inconclusive, contradictory and ever-

changing– Current scientific evidence is not absolute. Therefore, we

cannot give definitive answers.– Scientific method - descriptions of methodological limitations

and results can sound evasive.

• Complicated scientific Concepts:– Random events: 1% of all census tracts would have higher or

lower cancer rates simply by chance• No one has ever called me and said “… there’s too few cancers in

my neighborhood”.• public seemingly can only grasp concept if discussing the lottery.

Communicating Results to the Public, continued

• Epi & Stat Concepts– Often case and/or population numbers are too small for

appropriate statistical analysis, and we are unable to conduct analysis.

• sometimes viewed as demeaning the current number of cases.• sometimes viewed as evasive or manipulative.

– For environmentally based cancer concerns, we examine only related cancers not “all cancers” due to etiologic differences in cancers – often public thinks all cancers are germane.

– Causality - if cluster confirmed statistically, doesn’t mean cancer is due to a single causal pathway.

Communicating Results to the Public, continued

• Epidemiologists & Statisticians (us)– Objectiveness viewed as lack of empathy.– Expertise viewed as “Ivory Tower’ism”– We are not good at saying we don’t know

In Conclusion

• Cancer clusters DO occur in communities, but are difficult to investigate and nearly impossible to prove.– Our tools to investigate are crude and we often lack

pertinent information or time to see the natural history of events.• Cancer never 1st disease manifestation in true cluster• From exposure to diagnosis can be 20 – 50 years,

depending on carcinogen– Most prevalent cancers are not strictly caused by

environmental exposures – i.e., lung or prostate cancer– Ignorance: what we think is harmless today, tomorrow

we may learn is dangerous.• We must take responsibility and precautions to

safeguard our health.

For More Information on Cancer Clusters• ACS:

http://www.cancer.org/Cancer/CancerCauses/OtherCarcinogens/GeneralInformationaboutCarcinogens/cancer-clusters

• NIH: http://www.cancer.gov/cancertopics/factsheet/Risk/clusters • CDC: http://www.cdc.gov/nceh/clusters/ • ATSDR: http://www.atsdr.cdc.gov/csem/cluster/docs/clusters.pdf

Calculating Disease Risk

Harvard School of Public Health, Disease Risk Profile: http://www.diseaseriskindex.harvard.edu/update/hccpquiz.pl?lang=english&func=home&page=cancer_index

Thank You!