The association of age and familial risk in a case-control study of breast cancer.

To investigate the association of breast cancer risk, age, and family history of breast cancer, 779 breast cancer patients and 1,558 comparably aged control patients without cancer or a history of cancer were studied. All patients were admitted to Roswell Park Memorial Institute, Buffalo, New York between 1982 and 1987. After adjustment for the effects of other major breast cancer risk factors, no overall increase in risk for a history of breast cancer in a first-degree relative was observed among younger women. However, when the age at reported occurrence of breast cancer was considered, increased relative risk (RR) was observed when the affected first-degree relative was diagnosed at a young age (RR = 1.3). In contrast, among older patients, greater risk (RR = 1.9) was associated with diagnosis in a first-degree relative at an older age. Among patients aged 55 years or older, risk for reporting one first-degree relative with breast cancer was significant (RR = 1.8) and was greater when more than one first-degree relative was reported to have breast cancer (RR = 3.3). Bilaterality in an affected first-degree relative was associated with increased risk only among older patients (RR = 2.3). Other studies have observed various age-related effects, but the present research differs in that the authors studied both the age of the patient at risk and the age of the affected relatives across the full range of ages at which breast cancer occurs. These findings may have implications for the identification of populations for earlier initiation of routine screening and for laboratory investigation of the genetic etiology of breast cancer.