Cancer Clusters

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Page last updated 2/25/2026.

Group of cancer cells
Cancer is a disease where cells in your body grow out of control and spread to nearby tissue or other parts of your body. There are many types of cancer and each has its own causes, treatments, and outcomes.
 
A cancer cluster is when more people in a certain area and time have the same kind of cancer than expected to be seen.

 

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Cancer Cluster Criteria

A group of cancers cases is a cancer cluster when all criteria are met.

  • A greater than expected number of cancer cases:
    • When the observed number of cases is higher than what would typically be observed in a similar setting (in a group with similar population, age, race, or gender). 
  • Of the same (etiologically) related cancer cases:
    • Cancer cases are the same type, are within a family of tumors, or have the same cause/exposure.
  • Occur within a group of people:
    • The population the cancers are affecting is defined by demographic factors, such as race/ethnicity, age, and gender.
  • In a defined geographic area:
    • Boundaries of the area where cancer cases occur need to be defined carefully. Moving boundaries (e.g. making an area larger or smaller) might make it look more or less likely that a cancer cluster exists.
  • Over a specific period of time:
    • The number of cancer cases needs to be looked at over a specific time period when determining if there are more than the expected number of cases.

Until all criteria are met, the group of cancer cases is often called a suspect cancer cluster. The definition of a cancer cluster does not include anything about the cancers all having a common cause.

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Reporting

Cancer (CCR Title 17 §2593) is a reportable disease.

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Call the Epidemiology Unit at (619) 692-8499, or send an e-mail, for more information.