Additional examples of modifiable cancer risk factors include alcohol consumption (associated with increased risk of oral, esophageal, breast, and other cancers), physical inactivity (associated with increased risk of colon, breast, and possibly other cancers), and obesity (associated with colon,breast, endometrial, and possibly other cancers). Observational evidence shows associations between amount of alcohol consumption, physical inactivity, and obesity and increased incidence of certain cancers. More research is needed to determine whether these associations are causal and thus whether avoiding these behaviors would actually reduce cancer incidence. Other lifestyle and environmentalfactors known to affect cancer risk (either beneficially or detrimentally) include certain sexual and reproductive practices, the use of exogenous estrogens, exposure to ionizing radiation and ultraviolet radiation, certain occupational and chemical exposures, and infectious agents.
Food and nutrient intake have been examined in relation to many types of cancer. Case-control epidemiological studieshave suggested an association between high fruit and vegetable consumption and reduced risk of various cancers. The quality of this evidence, however, has been questioned, and prospective cohort studies exploring this question have shown inadequate evidence to conclude that such an association truly exists. Contrary to expectation, randomized trials found no benefit of beta-carotene supplementationin reducing lung cancer incidence and mortality; risk of lung cancer was statistically significantly increased in smokers in the beta-carotene arms of 2 of the trials. Similarly, randomized controlled trials have found no reduction in risk of subsequent adenomatous polyps of the colon in individuals who have had polyps previously resected taking dietary fiber supplements compared with thosereceiving much lower amounts of supplemental wheat bran fiber. Ecologic, cohort, and case-control studies have found that increased consumption of fat and red meat is associated with increased risk of colon cancer. A randomized controlled trial of dietary modification to lower fat consumption in postmenopausal women, however, showed no reduction in colon cancer. Likewise, there was no benefit of thelow-fat diet on all cancer mortality, overall mortality, or cardiovascular disease. A large randomized trial is currently underway to investigate whether men taking daily selenium or vitamin E or both experience a reduced incidence of prostate cancer in comparison with men taking placebo pills.
The rates of newly diagnosed cancer cases (incidence) are one way to measure progressagainst cancer. The lower the rates, the better.
Another important measure is the proportion of cancers diagnosed at a late stage. The stage of a cancer shows how far the disease has progressed. The earlier the stage at diagnosis, the better the chances for cure. Downward trends in the proportion of late cancer diagnoses are a sign that screening is working for the cancers for which early detectionmethods are available.
This section of the Cancer Trends Progress Report - 2005 Update provides data on the rates of new cancers, based on the NCI Surveillance, Epidemiology, and End-Results (SEER) Program, by cancer site and by racial and ethnic group. Also included are data on the proportion of cancers diagnosed at a late stage for five of the major cancer sites where cancer screening has been...