Epidemiologic determinants of the mammographic parenchymal pattern. A population-based study within a mammographic screening program.

Epidemiologic data and information on the mammographic parenchymal pattern (classified according to Wolfe (Cancer 1976;37:2486-92)) were obtained from 38,757 (89%) of all women who were invited to undergo mammography in a population-based screening program in Kopparberg County, Sweden, starting in October 1977. The prevalence of the high-risk patterns (P2 and DY) was significantly higher in women aged 46-50 years than in any younger or older age group. A univariate analysis revealed that the odds ratio (OR) of having a high-risk pattern increased regularly with increasing age at first birth and was highest in nulliparous women. These associations remained evident in all age groups and were most pronounced in the oldest women. A history of breast biopsy increased the likelihood of having a high-risk pattern (OR = 1.57), whereas a similar weak overall association with prior cancer in the contralateral breast (OR = 1.40) and with familiar occurrence of breast cancer (OR = 1.20) was eliminated when other confounding factors were considered in a multivariate analysis. The authors conclude that characteristics of the reproductive lives of women have a significant and lifelong impact on their mammographic parenchymal patterns.