Diagnostic Challenges and Pitfalls of Mammary Pleomorphic Adenoma Illustrated by a Case Report

Mammary pleomorphic adenoma is a biphasic tumor, characterized by epithelial-myoepithelial components with myxochondroid stroma, resembling the prototypic pleomorphic adenoma of the salivary glands. We report the multiple diagnostic pitfalls raised by a mammary pleomorphic adenoma, initially diagnosed as mucinous carcinoma on fine-needle aspiration (FNA) cytology and invasive carcinoma on needle core biopsy. The final diagnosis was made on the surgical specimen. As the term "pleomorphic" suggests, this tumor can present various phenotypes, some of which might be misleading on both FNA cytology or needle core biopsy. Rearrangements in PLAG1 and HMGA2 genes have not been detected in our patient. Mammary pleomorphic adenoma is considered a benign tumor, despite rare local recurrence and malignant behavior. Its correct identification, despite the difficulties, is essential to avoid unnecessary aggressive treatment.