A major risk factor for breast cancer is family history of the disease in first-degree relatives. This study evaluates the validity of family history information on breast cancer in mothers and sisters of breast cancer probands from the cancer registry (CR) compared to personal interviews (PI) of 359 consecutive population-based cases of breast cancer. Breast cancer is seen in mothers of 14% of probands by CR compared to 12% by PI. Further, 13% of probands have a sister with breast cancer using CR compared to 12% by PI. Using PI as the standard, the sensitivity of the CR family history data in mothers is 92% and the specificity is 99%, while in sisters they are 88% and 99%, respectively. These estimates were calculated on cases where family history information is available in the CR. Sensitivity and specificity are recalculated, recording an "error" whenever family history information is not available, and they are 75% and 68%, respectively, for mothers and 72% and 70%, respectively, for sisters. Estimates of proband-mother and proband-sisters familial breast cancer from CR and PI are sufficiently similar to warrant the use of CR family history data in studies of genetic epidemiology.
The family phenotype consistent with the BRCAl syndrome was found in four
(1.1 %) probands, all below age 50 years, while for BRCA 2 there were five (1.4%) probands, three below age 50 years and two 50 years or older. Site-specific familial breast cancer was found in 23 (6.4%) probands. Population-based multiple-case breast cancer families can rapidly be identified through CR. These families can make substantial contributions to the study of genetic and environmental etiology of the disease as well as benefit from preventive and therapeutic efforts. As new knowledge and tools in molecular genetics become available, there is an urgent need for large population-based registries of families at high risk for cancer.