Familial breast carcinoma risks by morphology: a nationwide epidemiologic study from Sweden

BACKGROUND: Familial risks in patients with breast carcinoma have not been assessed by morphologic types of medically verified cancers. Reliable data on familial risks would help to establish prevention programs and guide clinical decisions. METHODS: We used the nationwide Swedish Family-Cancer Database to calculate standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) for invasive and in situ breast carcinomas in women with mothers and sisters. This database has information on 10.2 million individuals and on more than 13,000 morphology-specific breast carcinomas. RESULTS: SIRs for all invasive breast carcinomas were 1.82 (95% CI 1.71-1.93) for breast carcinoma in the mother and 1.89 (1.70-2.01) for breast carcinoma in a sister. The respective risks were 1.81 and 1.85 for a mother and sisters with ductal breast carcinoma. The SIRs were equally for lobular, tubuloductal, comedo, and mucinous breast carcinomas. However, the SIRs for lobular carcinoma were lower than those for the ductal type, whereas the opposite trend was noted for the comedo and mucinous type; none of the differences were significant. The risks for all morphologic types were highest when both a mother and a sister were affected, SIR 3.19 (2.36-4.22). The risks for in situ breast carcinomas were 2.09 (1.78-2.44) for an affected mother, 2.24 (1.88-2.85) for an affected sister, and 5.23 (2.59-9.39) when both a mother and a sister were affected. CONCLUSIONS: The data suggest that the familial risk of breast carcinoma is independent of the morphologic type. The higher risks in in situ cancer may be due to medical surveillance. The risks were identical from a mother or sister proband, suggesting that recessive effects are unlikely as a heritable cause of breast carcinoma.