A cancer cluster is the occurrence of a greater than expected number of cases of a specific cancer within a community. The community of interest may be defined by geographic area, population, time period, worksite, etc. Cancer clusters may be suspected when several family members, friends, neighbors or co-workers have been diagnosed with cancer.
The priority in responding to a cancer cluster inquiry is determining whether an environmental, occupational or community-level exposure is associated with the cancer cases included in the inquiry. Some factors may indicate that an environmental exposure is associated with the cancer cases. These factors include: cases of one type of cancer, cases of a rare type of cancer, or cases among age groups that do not usually experience a specific cancer. In most instances, even when the number of cancer cases is greater than expected, no common exposure can be identified. This may occur for several reasons, including: 1) most cancer clusters are random occurrences unrelated to environmental exposures; 2) there is no known relationship between the cancer of interest and any identified environmental or occupational exposures; 3) important details about environmental exposures are missing and cannot be obtained; or 4) the number of cases involved in a cluster is too small to draw any meaningful conclusions.
Every year, the Oregon Health Authority (OHA) receives and responds to inquiries about suspected cancer clusters. OHA procedures for responding to cancer cluster inquiries are outlined in Responding to Cancer Cluster Inquiries