Download the original attachment



TO:  George Poitras

FROM: Francisco Meza, M.D., M.P.H., Gina Solomon, M.D., M.P.H., Natural Resources Defense Council

DATE:  April 9, 2010

RE:  Fort Chipewyan Cancer Cluster Investigation 

The study by Dr. Chen investigating the cancer cluster in Fort Chipewyan (Chen 2009) has several weaknesses, but was a good first step. It did not try to identify the cause of the cancer cluster, but did find a very significant increase in the cancer rate in Fort Chipewyan, 51 cancers when only 39 were expected. Specifically, the report identifies an increase in certain lymphomas/leukemias, and lung cancers in women. In general cancer cluster investigations are often unable to find significance due to the small sizes of the communities affected. Fort Chipewyan is a very small community, so it is striking to find a statistically significant increase in cancer with such a small sample size. It is easier to identify a cancer cluster if the cancer is rare, found in an unusual age group or mostly one type of cancer predominates.  

The finding of no increase in cholangiocarcinoma, as reported in the study, is misleading. There was an increase in biliary cancers. In our opinion, it is inappropriate to separate out the adenocarcinoma of the Ampulla of Vater, since it is essentially the same disease as cholangiocarcinoma. This is significant, because there are studies that indicate an environmental cause of these cancers. An occupational health study in Sweden found higher rates of biliary cancer in men employed in petroleum refining and chemical processing (Malker 1986). There have also been case reports of biliary cancer clusters in men exposed to hydrocarbon solvents (Zarchy 1998). There are good physiologic reasons to expect that chemicals such as polycyclic aromatic hydrocarbons would be associated with biliary cancers because these chemicals are excreted in the bile and are highly mutagenic, so the cells lining the biliary tract would be directly exposed to concentrated amounts of these chemicals.  

The report also identified two soft tissue sarcomas in the population of Fort Chipewyan. These are very rare and lethal cancers. One of the cases was a 26 year old man. This may have been a small number, but very significant for this extremely rare type of cancer in a small population. Dioxin exposure has frequently been associated with soft tissue sarcoma in the published scientific literature (Zambon 2007). 

There was also an increase in lung cancers only in women. Smoking rates are not completely covered in this report. Also, an exposure history of working in a uranium mine where they may have been exposed to radon gas may have been useful in evaluating exposure. This finding will require follow-up testing for radon gas in homes in this community. There are many studies showing that radon gas causes lung cancer (Frumkin 2001).  

Other research needed to characterize the excess leukemia and lymphoma includes assessment of exposure to benzene or polycyclic aromatic hydrocarbons (PAHs). Excess leukemia and lymphoma have been associated with exposure to petroleum products and hydrocarbons as well as dioxins (Bertazzi, 2001, Terry 2005).  

There are significant problems with the proposal of following up with a cohort investigation for those who have lived in Fort Chipewyan. A cohort study is likely to be inconclusive because the population of Fort Chipewyan is very small, and cohort studies require a large sample size in order to have adequate statistical power to identify any associations that may exist. A cohort study also is expensive and generally takes many years to complete. We would estimate that the design and execution of a cohort study in Fort Chipewyan would take at least ten years to complete. This is far too long to wait in a town with a confirmed public health epidemic of cancer. 

The best next step should be to evaluate the population of Fort Chipewyan for exposures to hazardous substances. The cluster evaluation showed an increase in cancer rates that may be linked to petroleum products, hydrocarbons, PAHs, radon, cigarette smoke, or dioxins. Prompt investigations of exposures are necessary to protect this population. Air sampling, water testing, soil evaluation, food sampling (fish and game), biological monitoring and occupational evaluations are necessary at this stage in the investigation. Questionnaires should also be designed to gather information about diet, occupation, smoking, water consumption, and other habits that could lead to exposure. Getting an environmental toxicologist or industrial hygienist with experience in these types of investigations would be helpful in protecting the health of the community.  

Lastly, the community of Fort Chipewyan was not involved in the Chen study. It is in the best interest of future researchers to be involved in the community and to address their concerns. The uranium in the mines, the arsenic throughout the environment and the oils sands waste were of significant concern to the population according to an article by CBC on 3/19/2020. These specific environmental exposures may increase the specific types of cancer found in the study and need to be investigated for the safety of the population of Fort Chipewyan. 


Bertazzi P, Consonni D, Bachetti S. 2001. Health Effects of Dioxin Exopsure: A 20-Year Mortality Study. American Journal of Epidemiology. V. 153 n. 11 1031-1044 

Chen Y, 2009. Cancer Incidence in Fort Chipewyan, Alberta, 1995-2006. Alberta Cancer Board Division of Population Health and Information Surveillance 

Franklin H, Samt J. 2001. Radon. CA Cancer Journal for Clinicians. 51:337 

Malker HS, McLaughlin JK, Malker BK. 1986. Biliary Tract Cancer and Occupation in Sweden. Br J of Ind Med. 43: 257-262 

Terry P, Shore D, Rausher G,Sandler P. 2005. Occupation, Hobbies and Acute Leukemia in Adults. Leukemia Research. Oct v 29 i10: 1117-1130 

Thun, Sinks MJ, Thomas.Understanding Cancer Clusters CA: A Cancer Journal for Clinicians. Vol. 54, number 5, September/October 2004 

Guidelines for Investigating Clusters of Health Events MMWR. July 27, 1990 Recommendation and reports  

Zambon P, Ricci P, Bovo E. 2007. Sarcoma Risk and Dioxin Emissions from Incinerators and Industrial Plants: A Case Control Study. Environmental Health. 6:19 

Zarchy T. 1998. Chlorinated Hydrocarbon Solvent and Biliary-pancreatic Cancer: Report of Three Cases. American Journal of Industrial Medicine v. 30 issue 3:341-2