Reproductive patterns and cancer incidence in women: a population-based correlation study in the USSR.

Many of the known or suspected risk factors of sex hormone-dependent cancers in women (low parity, delay in childbearing, etc) are typical features of modern reproductive behaviour. Within the USSR regional variations in principal reproductive characteristics and the incidence of breast and cervical cancers have been studied using standard correlation and regression analysis. The associations identified in previous analytical studies are generally present in the overall USSR population. However, the demographic peculiarities of this country (low mean ages at marriage and first birth, high rate of induced abortions, etc) introduce specificity into these relationships. The principal findings are: prevailing influence of parity versus age at first birth on regional variation of breast cancer incidence; consistent association between abortion rates (total, out-of-hospital and in primigravidas) and incidence of both breast and cervical cancers; suggested positive associations of early marriage and first birth with cervical cancer risk. Most of the reproductive variables studied affect the incidence of breast and cervical cancers in opposite ways.