Community cancer investigations

We collaborate with the Colorado Central Cancer Registry to respond to concerns about possible cancer clusters thought to be related to environmental risks.

  • A cancer cluster is a greater-than-expected number of cancer cases that occur within a group of people in a geographic area over a specific period. We use CDC guidelines to determine whether an excess number of cancers have occurred.
    • When a suspected cancer cluster has been identified, we investigate whether the cancer cases plausibly can be linked to some shared environmental exposure.

  • Data routinely collected by the cancer registry provide an important tool to respond to community and occupational concerns.

  • All cancers diagnosed in Colorado are reported to the registry with the exception of non-melanoma skin cancers.

  Publications and findings

Understanding cancer

Cancer is not a single disease but a group of more than 100 different diseases that share some common characteristics. Cancer is the second leading cause of death in Colorado and the United States. One out of every three people is expected to be diagnosed with cancer in their lifetime. Three of every five cancer deaths are due to tobacco use, obesity, lack of physical activity, and an unhealthy diet. The most common risk factors for cancer are:

  • Growing older
  • Tobacco
  • Excessive exposure to the sun
  • Ionizing radiation
  • Certain chemicals and other substances
  • Some viruses and bacteria
  • Certain hormones
  • Family history of cancer
  • Alcohol
  • Unhealthy diet, lack of physical activity, or obesity

Overall, a relatively small number of cancers are linked to toxic substances in the environment or workplace. Even when we know a substance can cause cancer, the risk of developing it depends on how much of the substance a person was exposed to and for how long.

How do you investigate cancers in a community?

When there is concern about cancer in a community, CDPHE works with local agencies to gather the information we need to investigate. This information includes details about the geographic area, possible environmental exposures, and specific cancer types.

We combine this information with data collected by the Colorado Central Cancer Registry. Hospitals, health care providers, and laboratories report cancer cases to the registry. These data enable us to determine how the number of cancer cases in the community compares to the average number expected based on Colorado cancer incidence rates.

What is the Colorado Central Cancer Registry (CCCR)?

The Colorado Central Cancer Registry analyzes cancer data. This data helps us answer important questions about cancer incidence, prevention, and treatment. Colorado state law and Board of Health rules require hospitals, clinics, health care providers, and laboratories to report this information to the Registry. The Registry collects data on all cases of cancer except non-melanoma skin cancer.

What is a cancer cluster?

Many cases of cancer occurring near each other are sometimes referred to as a “cluster.” People may report that several family members, friends, neighbors, or co-workers have been diagnosed with cancer.

After we investigate, we find most reported clusters are coincidences with no known causal connection. There are usually different kinds of cancer in the group, and the number of cases is typically close to the  expected. But sometimes, a cluster is related to public health factors that may place people at greater risk. These reports warrant further investigation.

What information do you require for a cancer investigation?

Case confirmation: We must confirm each reported cancer case in the community. We review medical information to gather details about the cancer case.

Type of cancer: Since cancer is many different diseases, we cannot analyze all types of cancer together as one group. Different kinds of cancer occur at different rates. So, it is important to consider the number of each type of cancer.

Study population: We define the study population by geographic boundaries, such as ZIP codes, or U.S. Census areas, such as, census tracts or block groups. By using geographic boundaries, we can get age, sex, and race/ethnicity population counts.

What happens when a cancer cluster is reported?

There are three possible outcomes:

  1. The numbers and types of cancer in the community are the same or similar to the expected results based on Colorado statewide cancer incidence. This outcome, while not definitive, means there probably is not any type of community-specific risk factor.
  2. While some kinds of cancer in the community are higher than expected based on Colorado statewide cancer incidence, there are clear differences in risk factors between the community and the state. For example, the community with more cancer cases also has higher rates of smoking or obesity than the Colorado average. It is usually impossible to determine whether the elevated numbers of cancer are due to a community-specific risk factor  (such as environmental exposure) or due to the differences in general risk factors (such as smoking, obesity, etc.).
  3. The number of specific kinds of cancer in the community are higher compared to expected based on Colorado statewide cancer incidence. There are no clear differences in general cancer risk factors between the study community and the comparison area. This outcome suggests a community-specific risk factor and further investigation.
What happens if cancer incidence is elevated in a community?

Our highest priority is to prevent disease and protect the health of all Coloradans. When a community has higher than expected rates of cancer, we provide technical help, data, and outreach to local agencies. Together, we work to find out why the cancer incidence is elevated in the community.

Where should I report a suspected community cancer cluster?

Report suspected clusters to the Colorado Central Cancer Registry. CCCR staff review medical records for each cancer patient to confirm the accuracy and completeness of the reports. We keep all patient, physician, and hospital information private and confidential, as required by state law.

Colorado Central Cancer Registry

What can I do to reduce my risk of getting cancer?

Adopt a healthy lifestyle. Avoid tobacco use, excessive alcohol consumption, and sun exposure.  Increase physical activity, maintain a recommended body weight, eat a healthy diet.  Take advantage of cancer screening. Doing all these things can greatly reduce your risk of getting cancer. Remember, even people who "do all the right things" sometimes still get cancer. One out of every three people is expected to be diagnosed with cancer in their lifetime.