Breast carcinoma etiology: current knowledge and new insights into the effects of reproductive and hormonal risk factors in black and white populations.

Abstract

A crossover in breast carcinoma incidence at ages 45-49 years has been observed between black and white women, with blacks experiencing higher incidence at younger ages and lower incidence after age 50 years. Can this phenomenon be partially explained by the differences in the distributions of reproductive risk factors? This article focuses on the effects and distributions of age at first full term pregnancy (FFTP), parity, and oral contraceptive (OC) use in younger versus older and black and white populations. Effects of hormone replacement therapy (HRT) are also summarized. A literature review was conducted and information integrated on the effects and distributions of reproductive and hormonal risk factors in black and white populations, the crossover effect of parity, and the Pike model of "breast tissue age." Overall, early age at FFTP and higher parity decreased risk for both races. Distributions of age at FFTP and parity varied widely between the two races. Based on the effects and distributions of age at FFTP and parity, the authors formulated the hypothesis that a crossover in incidence curves between the two races would be expected, rather than be considered an anomaly. Regarding OC use, generally a stronger increase in risk was observed for younger women than for older women. Regarding HRT, a recent meta-analysis observed an increased risk of 1.35 for 5 years of use or more. To promote public health in diverse populations, and to provide further insight into breast carcinoma etiology, research needs to focus on multicultural differences and similarities in the relation of hormonal risk factors and breast carcinoma.