Carcinoma of the breast with medullary-like features: diagnostic challenges and relationship with BRCA1 and EZH2 functions.

This case presentation reviews the histologic distinction between pure medullary carcinoma and breast carcinomas with medullary-like features. This particular case prompts us to analyze the relationship among medullary carcinoma, basal-like breast carcinomas and carcinomas associated with germline BRCA1 mutations. In addition to now well-defined features, such as expression of high-molecular-weight cytokeratins and EGFR (epidermal growth factor receptor), basal-like tumors have a deficiency or dysfunction of BRCA1. This association in part explains the histologic features of BRCA1-associated breast cancers. Recent studies in our laboratory demonstrate that BRCA1 protein is regulated by a recently described gene, EZH2. These concepts illustrate the important relationships among histopathologic features; genomic profile; single gene abnormalities, such as BRCA1 and EZH2; and growth regulation in this subset of breast carcinomas.