Relationship Between Relative Risk of Developing Breast Cancer and Absolute Risk in a Population of Rural, Older African American Women.

Abstract

Relative risks computed from known breast cancer risk factors can be used to quantitate a woman's individual risk of developing breast cancer. However, among older women the absolute risk of developing breast cancer over a specified time interval may be more useful in risk-benefit counseling. The objective of this investigation is to characterize the relationships between relative risks and absolute risks of breast cancer among a population of rural, older African American women. Among 224 African American women aged 50-91 years, relative risks were computed from historical information on age at menarche, number of previous biopsies, age at first birth, and number of first-degree relatives with breast cancer. These estimates, combined with the woman's current age, average remaining life expectancy, age-specific mortality, and breast cancer incidence rates, were used to estimate lifetime probabilities of developing breast cancer. Most women in the cohort (72.8%) had weak relative risks of 1.01-1.5 and only 3.5% of the women had relative risks of greater than 3.0. The majority of the women (87.5%) had lifetime probabilities of developing breast cancer that were less than 5%. Although there is a marked increase in age-specific breast cancer incidence with age, the probability of developing breast cancer in this population is low, primarily due to the low relative risks and the effects of competing mortality at older ages. Screening mammography should be directed toward women with high risks who are not receiving regular screening mammograms.