Low-grade adenosquamous carcinoma of the breast: A case with pathogenic germline mutation in the BRIP1 gene

Low grade adenosquamous carcinoma (LGAC) is an uncommon variant of metaplastic “triple negative” breast cancer with clinical-radiologic characteristics and histopathology which overlaps with other entities such as syringomatous adenoma. We report a case of LGAC in a woman in her 40s who presented with breast pain. An irregular hypoechoic retroareolar mass was identified on mammogram. Biopsy showed nests of cells with squamoid appearance and compressed “tadpole-shaped” glandular structures embedded in dense collagenous stroma with lymphoid aggregates. The tumor cells were highlighted by CK7 and squamous component by CK5/6 and p63 and were ER, PR and HER2 negative. The morphologic and immunophenotypic features were consistent with LGAC. Genetic study found she was heterozygous for the p.R798* pathogenic germline mutation in BRIP1 gene. Patient underwent excision and managed with adjuvant radiation alone post operatively. This is the first LGAC reported with BRIP1 mutation and we emphasize characteristics in diagnosis, differential diagnosis and management for LGAC in this report.