Multiple births and risk of breast cancer.

Data from a large, multicenter, population-based case-control study were analyzed to investigate the relation between multiple birth pregnancies and subsequent breast-cancer risk in the gravidas. Women less than 75 years old who had breast cancer were identified from statewide tumor registries in Wisconsin, western Massachusetts, Maine and New Hampshire. Controls aged less than 65 years were selected randomly from lists of licensed drivers, and controls aged between 65 and 74 were selected randomly from lists of Medicare beneficiaries. Information on reproductive history and other factors was obtained by means of telephone interviews. After excluding nulliparous women, 5,880 case subjects and 8,217 controls remained for analysis. Multiple birth pregnancies occurred in 146 cases and 218 controls. Adjusted for the number of full-term pregnancies and other confounders, the odds ratio (OR) for any multiple birth pregnancy was 0.94 (95% confidence interval, 0.75 to 1.17). The null association between multiple birth pregnancies and breast cancer remained if the mother's first pregnancy or last pregnancy resulted in a multiple birth. In addition, no trend in risk emerged for age at first multiple birth or time since last multiple birth. While other investigators have suggested biological mechanisms to explain both protective and detrimental effects of multiple births and subsequent development of breast cancer, this study does not support either assertion.

Strenuous physical activity in young adulthood and risk of breast cancer (United States).

The epidemiologic data on the relation between strenuous physical activity and breast cancer are limited and inconsistent. Because risk of breast cancer may be influenced by ovarian function which, in turn is modulated by physical activity, the hypothesis that exercise may be associated with a reduced risk of breast cancer merits further investigation. We, therefore, conducted a large case-control study in 1988-1991, and interviewed 6,888 women (17 to 74 years of age) with breast cancer in Maine, Massachusetts, New Hampshire, and Wisconsin (United States). Interviewed controls (9,539 women, 18 to 74 years of age) were selected randomly from lists of licensed drivers (for younger women) or from a roster of Medicare enrollees (for older women). We used multivariate adjusted odds ratios (OR) and 95 percent confidence intervals (CI) from logistic regression models to estimate relative risks between self-reported physical activity when 14 to 22 years of age and breast cancer. When compared with sedentary controls, women who reported any strenuous physical during ages 14 to 22 years had a modest reduction in the risk of breast cancer (OR = 0.95, CI = 0.93-0.97). However, those who exercised vigorously at least once a day had a 50 percent reduction in risk of breast cancer (OR = 0.5, CI = 0.4-0.7). These data support the hypothesis that women who are physically active have a reduced risk of breast cancer.

The association of body size and large bowel cancer risk in Wisconsin (United States) women.

Body size is associated with the risk of many diseases, including diabetes, heart disease, and some cancers. To evaluate the association of body size with large bowel cancer, height and weight measurements were ascertained by telephone interview from 779 Wisconsin (United States) women with newly reported diagnoses of carcinoma of the colon and rectum. Controls (n = 2,315) interviewed for this case-control study were selected randomly from Wisconsin driver's license files and Health Care Financing Administration files. The effects of weight and height were examined using multiple logistic regression to control for potential confounding variables. In this study, weight adjusted for height increased the risk of colon cancer (odds ratio [OR] for 72.57-148.33 kg cf 36.29-58.05 kg = 1.4, 95 percent confidence interval [CI] = 1.0-1.9) but did not increase the risk of rectal cancer. Height did not influence risk for cancer of either the colon or the rectum. Left-colon subsite analysis showed especially strong associations with current weight and with percent change in weight since age 18. These data suggest that a dose-response relationship exists between body size and risk of colon cancer in women; body size did not appear to influence risk of rectal cancer.