History of the Cancer Prevention Studies
The American Cancer Society’s intramural research program was founded in 1946 under the direction of E. Cuyler Hammond. From the 1940’s through 2008, epidemiology was part of a larger program that included cancer surveillance research. The Epidemiology Research program became a separate intramural program in 2009, due to growth and diversification of activities in the two programs. It is now one of six intramural research programs supported by the Society.
In 1952, epidemiologists at the Society launched the Hammond-Horn Study, a large, long-term follow-up study designed to examine the association of cigarette smoking with death rates from cancer and other diseases. For that study, 22,000 volunteers recruited a cohort of 188,000 men who provided detailed information on their smoking habits. These men were followed for mortality through 1955. This study helped to establish cigarette smoking as a cause of death from lung cancer and coronary heart disease. The study also demonstrated the Society’s ability to conduct very large prospective cohort studies, and paved the way for subsequent Cancer Prevention Studies. (Cancer Prevention Studies – Overviews)
Briefly, in 1959, the CPS I cohort was established and included nearly 1 million men and women recruited by 68,000 volunteers in 25 states. Participants were followed for mortality through 1972. Results from the CPS I cohort clearly demonstrated that the sharp increase in lung cancer death rates among US women between 1959 and 1972 occurred only in people who smoke, and was the first study to show a relationship between obesity and shortened overall survival.
In 1982 the CPS II cohort was established through recruitment of 1.2 million men and women by 77,000 volunteers in 50 states, the District of Columbia and Puerto Rico. Similar to the previous cohorts, CPS II participants were initially followed only for mortality. Mortality follow-up of the entire CPS-II cohort continues with biennial linkage to the National Death Index. The more than 480,000 people who never smoked in CPS-II provide the most stable estimates of lung cancer risk in the absence of active smoking. CPS-II data are used extensively by the Centers for Disease Control and Prevention (CDC) to estimate deaths attributable to smoking.
The CPS II Nutrition Cohort was established in 1992-1993 as a subgroup of the larger CPS II cohort, with the primary goal of following enrollees for cancer incidence in addition to mortality. Approximately 185,000 men and women responded to a 10-page mailed questionnaire and this subcohort has been followed biennially for cancer incidence, as well as mortality, since 1992. Data from the CPS-II Nutrition Cohort has been particularly valuable for clarifying associations between cancer risk and obesity, physical activity, diet, use of aspirin, and or hormone use, among other factors. The CPS II Lifelink Cohort was initiated in 1998 with the goal of collecting and storing blood samples from approximately 40,000 members of the CPS II Nutrition Cohort. An additional 70,000 Nutrition Cohort participants provided mouthwash samples for the collection of buccal cell DNA. The Lifelink Cohort was established to create a repository of serum, plasma, red blood cells, and DNA for future analyses. This valuable resource has allowed Society investigators and their collaborators at other institutions to study how genetic, hormonal, nutritional and other factors measured in blood are related to the occurrence and/or progression of cancer.
While landmark findings from the CPS II cohort have informed multiple areas of public health policy and clinical practice, the cohort is aging. A new cohort is needed to explore the effects of changing exposures and to provide greater opportunity to integrate biological measurements into studies of genetic and environmental risk factors. Therefore, in 2006, Society epidemiologists began the enrollment of a new cohort, CPS-3. All participants are providing blood samples at the time of enrollment. Following on the long-history of partnering with Society volunteers and supporters for establishing a cohort, the Society’s community-based Relay For Life fund-raising events are the primary venue for recruiting and enrolling participants. Indeed, the blood specimens and questionnaire data collected from CPS-3 participants will provide unique opportunities for future research in the United States.
Contributions of the Cancer Prevention Studies
The Cancer Prevention Studies have provided unique contributions both within the American Cancer Society and in the global scientific community. These contributions allow the Society to focus its resources on factors most important in preventing cancer and promoting health. In particular, the data collected in these studies provided a unique picture of the progression of the tobacco epidemic and the emergence of the obesity epidemic over the last half- century. Some other key findings from these studies include:
- Cigarettes with reduced yield of tar and nicotine do not reduce the risk of lung cancer.
- Obesity is associated with increased death rates from at least ten cancer sites, including colon and post-menopausal breast cancer.
- Discovery of the link between aspirin use and lower risk of colon cancer opened the door to research on chronic inflammation and cancer.
- Relationships of other potentially modifiable factors such as physical inactivity, prolonged hormone use and certain dietary factors with cancer risk.
- Air pollution, especially small particulates and ozone, increase death rates from heart and lung conditions. CPS-II findings helped to motivate the Environmental Protection Agency to propose more stringent limits on air pollution.