Cancer Data Inquiries

See Frequently Asked Questions at the bottom of the page.

Community Cancer Concerns Information Sheets are also available in English and Spanish.

The Oregon Health Authority (OHA) Public Health Division reviews questions from the public about cancer patterns in communities and workplaces. A cancer data inquiry is when someone asks OHA to look at available cancer data to see if the number of cases in a specific place or group is unusual. Many people contact OHA when they notice several cancer cases among coworkers, neighbors or family members and want to know whether it could be related to something in the environment.

How OHA responds to cancer concerns

A cancer cluster is a higher‑than‑expected number of the same or closely related cancers occurring among a group of people in a specific place and time.

When OHA receives a concern about a possible cancer cluster, the Cancer Inquiries Review Team (CIRT) gathers information and reviews the available data. They look at:

the type of cancer
when the cancer cases occurred
who was affected
whether the situation meets national definitions for a possible cancer cluster

Most suspected clusters happen by chance or are not related to harmful environmental exposures. National reviews show that it is rare for cancer cluster investigations to find an environmental cause. Because cancer is common and becomes more likely as people age, cases can sometimes appear “grouped together” even when there is no shared cause.

What OHA looks for

To decide whether a formal cancer rate analysis would be helpful, OHA considers:

Whether the cancer type is uncommon, since common cancers have many possible causes.
Whether the cancers are the same type or are linked to the same known exposures.
Whether the cases occurred in a defined geographic area and time.
Whether there are at least five cases to produce reliable statistics; very small numbers often reflect random variation.

Clear and consistent patterns are needed for meaningful review. A small number of cases spread over many years or involving different cancer types cannot show a trend.

If an environmental contaminant is already known and is being addressed by environmental agencies, cancer rate analyses usually does not provide additional useful information that will protect the public’s health.

What cancer data can and cannot tell us

The Oregon State Cancer Registry (OSCaR) documents all new cancer diagnoses and tracks cancer rates and trends over time. But these data have some limitations:

They do not include lifestyle or personal history details, such as smoking or job‑related exposures.
Reporting may take up to two years, so data are not real time.
Cancer rate analyses cannot explain why a specific person developed cancer.

Cancer data can show patterns in communities, but they cannot tell us what caused one person’s cancer. Looking at small areas, such as a single neighborhood, can also produce unusual looking results simply by chance.

Why work-related cancer investigations are especially challenging

Workplace cancer concerns are difficult to investigate. Certain workplace chemicals, like asbestos, can be clearly linked to a specific type of cancer but this is uncommon. Below are some reasons why workplace cancer concerns are challenging to evaluate:

Most cancers are caused by many risk factors, including age, personal history and exposures outside of work.
Coworkers of similar age may develop cancer around the same time simply because they are aging together.
Most cancers develop slowly over many years, making it hard to know whether workplace exposures played a role.

Reviews of workplace cancer concerns rarely find a cancer cluster or a link to a specific exposure.

When investigations move forward

Concerns that meet Oregon’s criteria—such as the type of cancer, the number of cases, the timing, and whether the environment could be involved—may be recommended for a formal cancer rate analysis.

If the criteria are not met, the inquiry is closed, and an explanation of the review and decision is provided.

We understand how stressful and frightening it can feel when several people you know are diagnosed with cancer. We care deeply about the health of people in Oregon, and we take every concern seriously. Unfortunately, cancer is common, and when the criteria listed above are not met, a cancer investigation is unlikely to help protect people’s health. This is especially true when environmental contaminants of concern are already known and agencies are actively working with the community.

If you have concerns about air quality, visit Cleaner Air Oregon to learn more about air toxics.

For concerns about hazardous waste sites or environmental exposures, explore Environmental Health Assessments for additional information.

Additional information about community cancer concerns (English)
Información adicional sobre las preocupaciones comunitarias relacionadas con el cáncer (en español)

Past Cancer Inquiries

Email: oscar.ohd@dhsoha.state.or.us

► Frequently Asked Questions (click to expand)

What is cancer and a cancer site?

Cancer is a term for hundreds of different diseases that all share one thing in common: some of the body’s cells begin to grow out of control. Sometimes these cells form lumps called tumors, and sometimes they spread into other parts of the body, which can make the disease life‑threatening.

A cancer site is the place in the body where the cancer first started. For example, if cancer begins in the lung, the lung is the cancer site even if the cancer later spreads to other organs.

What is a cancer cluster?

A cancer cluster is a higher‑than‑expected number of the same or closely related types of cancer occurring among a group of people in a specific place and time.

What isn’t a cancer cluster?

Not every situation where several people have cancer at the same time or in the same place is a cancer cluster. Many patterns that look unusual are actually expected. A situation is not considered a cancer cluster when:

the cancers are different types that are not linked to the same causes
the number of cases is what would normally be expected for a community of that size
the people affected are of similar age and developing cancer as part of normal aging
the cases occurred over many years and are not grouped in time
the cancers can be explained by common risk factors, such as smoking, family history, or exposures outside the area or workplace

In many situations, cancers appear “grouped together” simply by chance, especially in small neighborhoods, small workplaces, or among people of similar ages.

What cancers are “common”?

In Oregon in 2023, the following cancer sites made up about 75% of all cancer cases:

Breast (female)
Prostate (male)
Lung and bronchus
Colon and rectum (colorectal)
Melanoma of the skin
Urinary bladder
Non‑Hodgkin lymphoma
Uterine corpus (endometrial; female)
Pancreas
Leukemia
Thyroid

These are considered Oregon’s common cancers. The cancers from breast through melanoma account for nearly 55 percent of all cancers diagnosed in Oregon.

Do most cancer cluster investigations find an environmental cause?

No. Most investigations do not find an environmental cause. When a cause is identified, it is usually related to workplace, residential, or lifestyle factors. Workplace exposures to chemicals, such as asbestos, show why strong safety measures are important.

Lifestyle choices also play a major role in cancer prevention. These include quitting tobacco, limiting alcohol, eating a balanced diet, staying active, and protecting skin from UV exposure.

Using environmental protections, workplace safety measures, and healthy habits together is the most effective way to help reduce cancer risk.

Why are common cancers usually not investigated?

Common cancers have many possible causes and become more common as people age. A higher number of these cancers in a community may happen by chance or because of age, health, or other common risk factors—not because of a harmful exposure.

Can cancer data tell me why someone I know got cancer?

No. Cancer rate analyses cannot determine why any one person developed cancer and cannot show personal causes.

Why can “neighborhood cancer rate” maps be misleading?

In very small areas, the numbers can jump around a lot from year to year. A spike in one neighborhood may simply be due to chance and may not mean anything is wrong.

What information does OHA need to review a cancer concern?

OHA needs the following details to review a cancer concern:

the specific type of cancer involved
whether that cancer type is uncommon
a clear location where the cases occurred
a defined period when the cases happened
at least five confirmed cancer cases, which helps ensure the statistics are reliable

What happens if the criteria aren’t met?

If Oregon’s criteria aren’t met or the review is unlikely to find meaningful results, OHA closes the inquiry and explains the review and decision.

What if there is already a known harmful substance in the environment?

If Oregon’s criteria aren’t met, or if the review is unlikely to produce meaningful results, OHA closes the inquiry. OHA then explains what was reviewed and how the decision was made.

What is OSCaR data (the cancer registry) used for?

The Oregon State Cancer Registry (OSCaR) collects information on all new cancer diagnoses in the state. This data is used to:

connect people with cancer to research studies that aim to improve cancer treatment
track cancer rates and trends over time in Oregon
evaluate how well cancer screening and prevention programs work

The Cancer Analysis Team uses OSCaR data to review concerns about cancer.

What should I do if I’m concerned about environmental exposures?

For concerns about hazardous waste or possible toxic exposures, visit OHA’s Environmental Health Assessments.

Why does OHA take this careful, step‑by‑step approach?

Questions about cancer and the environment are serious, and OHA treats them seriously. This careful process helps ensure that any investigation is thorough, useful, and as effective as possible.