Familial breast cancer in a normal population

Family histories of cancer of all anatomical sites, with particular emphasis upon carcinoma of the breast, were evaluated in more than 4000 consecutive persons independently, at medical centers in Omaha (Group I, 3261 patients) and Detroit (Group II, 1058 patients). Findings in both groups were strikingly similar. Approximately one half of all families did not manifest cancer; approximately 1/3 had cancer in a single first degree relative, while slightly more than 20% had cancer in 2 or more first degree relatives. Only 7% had cancer in 3 or more first degree relatives. Approximately 9.1% of lineages in Group I and 7.4% in Group II had a single member with breast cancer, while approximately 0.7% of lineages in Groups I and II had 2 or more first degree relatives with breast cancer. Familial tumor associations with breast were observed, with statistical significance found for breast and prostate cancer (p <0.005 in Group I, p <0.25 in Group II, and p <0.005 when the 2 groups were combined). Implications for carcinogenesis and cancer control are discussed.