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Objective: We examined breast cancer risk related to lifetime exposure to oral contraceptives (OCs) and hormone replacement therapy (HRT) in postmenopausal women., Methods: The Women's Contraceptive and Reproductive Experiences (CARE) Study was a population-based case-control study that included 1847 postmenopausal women with incident invasive breast cancer, and 1932 control subjects, identified using random digit dialing., Results: 45% of cases and 49% of controls used both OCs and HRT. OC users were not at increased risk regardless of subsequent HRT exposure. HRT users who had used OCs previously did not have a higher risk of breast cancer than women with no exposure to OCs. We observed a negative interaction (p-value: 0.032) of combined hormone replacement therapy (CHRT) and past OC use. The increase in risk with CHRT was stronger in women who had never used OCs in the past (odds ratio: 1.05; 95% confidence interval: 1.01-1.10 per year of exclusive CHRT use) than in women who had used OCs (odds ratio: 1.00; 95% confidence interval: 0.97-1.03)., Conclusions: We found no indication that adverse effects of exposure to OCs or HRT appeared only in the presence of the other hormone or were exacerbated by exposure to the other hormone.

To evaluate whether recreational physical activity is associated with breast cancer among young women, the authors analyzed data from a population-based case-control study. Cases (n = 1,668) were women under age 45 years who had been newly diagnosed with breast cancer between 1990 and 1992 in Atlanta, Georgia, central New Jersey, or Seattle, Washington. Controls (n = 1,505) were frequency-matched to cases by 5-year age group and geographic area of residence. Breast cancer was not associated with recreational activity in any of the three time periods assessed (highest quartile of activity vs. lowest: age- and center-adjusted odds ratio (OR) = 0.94 (95% confidence interval (CI) 0.77-1.15) at ages 12-13 years, OR = 1.08 (95% CI 0.88-1.32) at age 20 years, and OR = 1.18 (95% CI 0.97-1.44) during the past year), with the average of the three time periods (OR = 1.02, 95% CI 0.84-1.25), or with daily climbing of at least two flights of stairs (without stopping) during the past year (daily climbing vs. never climbing: OR = 1.03, 95% CI 0.86-1.23). Estimates were not modified or confounded by body mass index, menopausal status, or caloric intake during the past year. These results do not support a protective role for physical activity in the risk of breast cancer among young women.

Data from a population-based case-control study of chronic lymphocytic leukemia were analyzed to assess the possible etiologic role of chronic antigenic stimulation. The study, conducted in four geographic areas of the United States (the metropolitan areas surrounding Seattle, Washington, Salt Lake City, Utah, Detroit, Michigan, and Atlanta, Georgia) sought to identify all incident cases (n = 430) among residents diagnosed between July 1, 1977 and December 31, 1981. The responses of these cases to questions about possible sources of antigenic stimulation were compared with the responses of controls selected from the populations of these areas. Little difference between cases and controls was present for a history of most forms of viral and bacterial infection and for a history of allergies or allergy treatment. However, a relation was observed with antecedent syphilis infection (odds ratio (OR) = 5.0, 95% confidence interval (Cl) 2.0-12.9). Associations of smaller magnitude were observed with a history of tuberculosis (OR = 1.9, 95% Cl 1.0-3.7) and of urinary tract infection (OR = 1.4, 95% Cl 1.1-1.9). Overall, however, the authors found little evidence of a relation between chronic antigenic stimulation and the occurrence of chronic lymphocytic leukemia. Nonetheless, because the measure of prior antigenic stimulation was restricted to that obtained through interviews and undoubtedly was an insensitive one, these negative results should not be interpreted as ruling out antigenic stimulation as a possible cause of some cases of chronic lymphocytic leukemia.