The histologic phenotypes of breast carcinoma occurring before age 40 years in women with and without BRCA1 or BRCA2 germline mutations: a population-based study.

Women with breast carcinoma diagnosed before age 40 years have a greater prevalence of germline BRCA1 and BRCA2 mutations than women with breast carcinoma diagnosed at older ages. Several recognizable histologic characteristics have been identified in breast carcinoma from studies of BRCA1/2 mutation carriers who belong to multiple-case families. The authors attempted to determine whether breast carcinoma occurring before age 40 years in BRCA1 or BRCA2 mutation carriers who were not selected for family history could be distinguished histologically from one another and from breast carcinoma in women of a similar age without a germline BRCA1 or BRCA2 mutation. The study undertook a histologic assessment of breast carcinomas diagnosed before age 40 years identified from a population-based study. Breast carcinoma in BRCA1 mutation carriers was associated with a distinct histologic appearance; these tumors were high grade, and had exceptionally high mean mitotic counts, a syncytial growth pattern, pushing margins, and confluent necrosis. Atypical medullary carcinoma was overrepresented in BRCA1 mutation carriers. All low grade tumors and tumors with low mitotic rates belonged to the group without BRCA1 or BRCA2 mutations. Pleomorphic lobular carcinomas and extensive intraduct carcinomas were more common in BRCA2 mutation carriers. Breast carcinoma occurring in women with a germline BRCA1 or BRCA2 mutation have recognizable histologic phenotypes, which may be useful in identifying individuals more likely to carry germline mutations. Histologic examination of breast carcinoma should become an important part of the evaluation of women seeking genetic testing for germline mutations in these breast carcinoma susceptibility genes.