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Cancer clusters

A cancer cluster is a greater-than-expected number of cancer cases within a group of people in a certain geographic area over a period of time.

A cancer cluster may be suspected if several family members, friends, neighbours or co-workers are diagnosed with similar types of cancers. However, what seems to be a cluster may actually be the expected number of cancer cases for that group of people, especially if the types of cancers that develop are common.

Key facts about cancer and cancer clusters

It is important to remember some key facts about cancer and cancer clusters:

  • Cancer is more common than most people think and affects many Canadians.
  • Cancer is a general term for a group of over 200 related but different diseases.
  • Different types of cancer often have different risk factors. For example, exposure to asbestos is a major cause of mesothelioma, but not breast cancer.
  • A cancer cluster may be due to chance alone.
  • The causes of cancer clusters are rarely found.

A cancer cluster may be present if a greater–than-expected number of cancer cases develop that involve:

  • one type of cancer
  • a rare type of cancer
  • a type of cancer develops in a group of people that don’t normally get that cancer (for example, children or young adults develop a cancer that usually develops in adults)

Cancer is more likely to occur as people get older. Because people are living longer, more cases of cancer can be expected in the future. This greater life expectancy may make it seem like cancer is becoming much more common, but the increase in the number of cancer cases is likely related to the growing number of elderly people in the population.

Investigating cancer clusters

At this time, Canada doesn’t have a federal agency that investigates possible cancer clusters. Provincial and territorial agencies collect and monitor cancer incidence statistics. The Canadian Cancer Society works with provincial, territorial and federal governments to analyze national cancer incidence and mortality data. The results are published each year in the Canadian Cancer Statistics. Provincial health agencies, provincial cancer registries or cancer agencies may have a protocol in place for investigating suspected cancer clusters.

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