Historical examples of work-related cancer clusters are well documented in the medical literature. Notable examples include: scrotal cancer among chimney sweeps in 18th century London; osteosarcoma among female watch dial painters in the 20th century; skin cancer in farmers; bladder cancer in dye workers exposed to aniline compounds; and leukemia and lymphoma in chemical workers exposed to benzene.
Cancer cluster suspicions usually arise when members of the general public report that their family members, friends, neighbors, or coworkers have been diagnosed with the same or related cancers. State or local health departments will investigate the possibility of a cancer cluster when a claim is filed. In order to justify investigating such claims, health departments conduct a preliminary review. Data will be collected and verified regarding: the types of cancer reported, numbers of cases, geographic area of the cases, and the patients clinical history. At this point, a committee of medical professionals will examine the data and determine whether or not an investigation (often lengthy and expensive) is justified.
In the U.S., state and local health departments respond to more than 1,000 inquiries about suspected cancer clusters each year. It is possible that a suspected cancer cluster may be due to chance alone; however, only clusters that have a disease rate that is statistically significantly greater than the disease rate of the general population are investigated. Given the number of inquiries it is likely that many of these are due to chance alone. It is a well-known problem in interpreting data that random cases of cancer can appear to form clumps that are misinterpreted as a cluster.
A cluster is less likely to be coincidental if the case consists of one type of cancer, a rare type of cancer, or a type of cancer that is not usually found in a certain age group. Between 5% to 15% of suspected cancer clusters are statistically significant.
In 2007 the Associated Press reported a confirmed cancer cluster in Delaware,
Delaware health officials have confirmed what residents near a coal-fired power plant long suspected: there is a cluster of cancer cases near the Indian River Power Plant. The News Journal reported Sunday that the rate of cancer cases in the area is 7 percent higher than the national average...The state study was released last month to Lt. Gov. John Carney, who requested the report.."
The same article noted that "the Division of Public Health is unlikely to study the matter further. The Department cited a lack of resources" as well as the difficulty of "pinning down" a precise environmental cause. The findings were reported elsewhere.
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- Pub Med - latest standards for evaluating cancer clusters
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- Australian Story about a cluster of breast cancer cases in the workplace