Although cancer is a serious and frightening diagnosis, it is a common disease. Current information shows that approximately one out of three Americans will develop cancer in their lifetime, and cancer will affect three out of four families. The risk of developing cancer increases with age, so as the population ages, more cases of cancer are expected in our communities.
The term cancer covers not one, but many diseases that share the common feature of abnormal cell growth. It can occur in almost any part of the body. Each cancer type develops differently and has different risk factors. For example, the main risk factor for lung cancer is cigarette smoking, but for skin cancer it is sun exposure. The causes of some common cancers such as breast cancer are still unknown.
Many people believe that something in the environment causes most cancers, but behavior and lifestyle accounts for most of the known cancer risks. Factors such as smoking, poor diet, obesity, heavy alcohol use, sexual and reproductive history, and genetic factors can all contribute to developing cancer. It is estimated that less than 10% of cancers are caused by environmental exposures. In contrast, cigarette smoking alone causes about 30% of cancers. In addition, family history is important and contributes to some types of cancer.
Most cancers take a long time to develop. It is usually decades from the time someone is exposed to something that might cause cancer to the time that cancer is diagnosed. This is one of the reasons that cancer is more common in older adults. In addition, the few chemicals that are linked to cancer must have fairly long and/or concentrated exposures before they may cause cancer.
Cancer Clusters
A cancer concern is defined as a greater than expected number of cancer cases that occurs within a group of people in a defined geographic area over a specified period of time. When people learn that several friends, family members, or neighbors have found out they have cancer, cancer concerns are often suspected. Cancer concerns are also sometimes suspected when people who work at the same place or have other factors in common get cancer.
If a suspected concern includes cancers of different types, it is probably not a “true” cancer concern. For example, if someone reported that there were many people with cancer in their community, but the kinds of cancer included lung, breast, leukemia, and prostate which are cancers known to have different risk factors; this would not be considered a cancer concern.
A confirmed cancer concern is a relatively rare occurrence and few documented concerns have been able to be linked to an environmental agent. To be a cancer concern, a group of cancer cases must meet the following criteria. Until all of these parameters are met, the group of cancer cases is often referred to as a suspected cancer concern.
greater than expected number
A greater than expected number is when the observed number of cases is higher than one would typically observe in a similar setting (in a group with similar population, age, race, or gender). This may involve comparison with rates for comparable groups of people over a much larger geographic area (e.g., an entire state).
Cancer cases
All of the cases must involve the same type of cancer or types of cancer scientifically proven to have the same cause.
Occuring within a group of people
The population in which the cancers are occurring is carefully defined by factors such as race/ethnicity, age, and gender for purposes of calculating cancer rates.
In a geographic area
Both the number of cancer cases included in the concern and calculation of the expected number of cases can depend on how we define the geographic area where the concern occurred. The boundaries must be defined carefully. It is possible to “create” or “obscure” a concern by selection of a specific area.
Over a period of time
The number of cases included in the concern, and calculation of the expected number of cases, will depend on how we define the time period over which the cases occurred.
What is a Cancer Cluster Investigation?
It is important to keep in mind that most investigations of suspected cancer concerns do not lead to the identification of an associated environmental contaminant. There are several steps taken, each with an increasing amount of resources needed, to investigate a possible cancer concern. To learn more about the detailed plan (or protocol) the Florida Department of Health uses the 2013 Cancer Concern Guidelines.
- Initial Contact and Response – The purpose of this step is to collect information to determine if additional follow up is warranted. Information should be collected about:
- The number(s) and type(s) of cancers – Different types of cancer have different causes. If the cancers reported are different, this is an indication that it is not a concern. Also, some cancers are common and may not be an indication of a concern.
- Demographic information of each person with cancer (e.g., age, race/ethnicity, and sex)
- Geographic area of concern
- Time period of concern
- Environmental hazard of concern – Need to determine if the environmental hazard has been shown to cause cancer and if the community was exposed to the hazard at an amount that would be of concern.
- Assessment – The purpose of this step is to determine whether the suspected cancer concern is statistically significantly higher than what would be expected. This step uses existing data and requires the determination of the study population, the cancer type(s), comparison population, and statistical methods to be used.
- Determining the Feasibility of Conducting an Epidemiologic Study – The purpose of this step is to gather additional information to assess the feasibility of conducting an epidemiologic study to determine whether the cases are associated with a common etiological risk factor (cause). If feasible, the outcome of this step should include a recommended study design.
- Conduct an Epidemiologic Investigation – The purpose of this step is to determine if the exposure to a specific risk factor or environmental contaminant might be associated with the suspected cancer concern.
At the end of each step, the information gathered is assessed and a determination is made about whether or not to move to the next step. Each step has criteria to help determine if the next step is warranted.
Limitations of Cancer Data
There is an inherent delay in collecting cancer incidence data. Each facility, laboratory, and practitioner is required to report to the Florida Cancer Data System within six months of each diagnosis and within six months of the date of each treatment.
Data are linked annually to mortality and hospital discharge databases respectively to find any missed cancer report. Consequently, a complete diagnosis year file is not available for surveillance activities and analysis until approximately two years after the close of the year (e.g., the 2015 cancer diagnosis file is available at the earliest January 1, 2018).