Association of the BRCA1 missense variant R1699W with a malignant phyllodes tumor of the breast

Familial breast carcinomas that are attributable to BRCA1 or BRCA2 mutations have characteristic morphologic and immunhistochemical features. BRCA1-associated carcinomas are poorly differentiated infiltrating ductal carcinomas frequently exhibiting morphologic features of typical or atypical medullary carcinomas such as prominent lymphocytic infiltrate and pushing margins. We report on a patient carrying the deleterious BRCA1 germline mutation R1699W, who presented with a malignant phyllodes tumor of the breast. The re-investigation of archival material by a reference pathologist of the German Consortium for Hereditary Breast and Ovarian Cancer (GCHBOC) revealed BRCA-associated pronounced pushing margins. In a total of 618 unrelated index patients who are registered in the GCHBOC database, no other phyllodes tumor has been described, while 10 carriers of the R1699W mutant have been identified. We conclude that the histopathologic appearance of the phyllodes tumor indicates an association with the BRCA1 mutation R1699W although it is a rare event in BRCA-positive families.