Breast cancer in relation to early use of oral contraceptives. No evidence of a latent effect
J. J. Schlesselman, B. V. Stadel, P. Murray and S. Lai
Department of Preventive Medicine and Biometrics, Uniformed Services University of the Health Sciences, Bethesda 20814.
A long-term effect of oral contraceptives (OCs) on breast cancer risk has
been suggested as an explanation for some studies' failure to detect an
association between OCs and breast cancer. To address this latency
hypothesis, we analyzed data on 4714 case subjects and 4540 control
subjects from the population-based Cancer and Steroid Hormone Study. No
support was evident for a latent effect of OCs on breast cancer risk
through age 54 years: among parous women who had cumulated more than six
years of OC use before their first term pregnancy, the risk of breast
cancer, relative to nonusers before first term pregnancy, was 0.6 at zero
to four years after first term pregnancy (95% confidence interval [Cl], 0.2
to 1.8), 0.7 at five to nine years (95% Cl, 0.3 to 1.7), and 1.1 at ten to
14 years (95% Cl, 0.3 to 3.9). Among nulliparous women with more than six
years of OC use in total, the relative risk of breast cancer, by interval
from last use of OCs, was 1.3 at zero to four years (95% Cl, 0.8 to 2.0),
1.1 at five to nine years (95% Cl, 0.5 to 2.0), and 0.6 at ten to 14 years
(95% Cl, 0.1 to 3.7).
