Characteristics of familial breast cancer in sweden: Absence of relation to age and unilateral versus bilateral disease

A case-control study was conducted to examine the hypothesis that familiality in breast cancer is a heterogeneous entity. A study of 1330 women, recently diagnosed as having breast cancer, compared, by paired sampling from a population register, the same number of age-matched women without a history of breast cancer. Data obtained by mailed questionnaires revealed a familial history in a first-degree relative in 149 patients and 90 controls (standardized relative risk/SRR/ = 1.7). The figures for second degree relatives were 115 and 81, respectively (SRR = 1.5). A detailed analysis of age at diagnosis and the occurrence of bilateral disease in the probands and their first-degree relatives with breast cancer failed to confirm any significant trend towards characterization of familial cases by early occurring or bilateral disease. The SRR for breast cancer in a first-degree relative was 1.7 for women with unilateral disease and 2.2 for those with bilateral. A slightly higher but nonsignificant relative risk was found for women diagnosed before (SRR = 2.4) than after (SRR = 1.7) 50 years of age. Familial cases did not run a higher risk of developing bilateral disease than nonfamilial—6 and 5%, respectively. No patient or control reported premenopausal and bilateral disease in her mother, whereas three patients and five controls reported these characteristics in one of their sisters. The correlation between age at diagnosis in familial patients and their mothers or sisters with breast cancer was low—0.38 and 0.29, respectively—and there was no correlation with respect to the occurrence of bilateral disease within the families.