Clear cell hidradenoma of the male breast: A case report and literature review

Introduction: Clear cell hidradenoma (CCH) is a rare type of benign breast tumor that may undergo malignant transformation in a few cases. It clinically manifests as a painless breast mass, and may include nipple discharge. Complete surgical excision with adequate safety margins is the primary treatment.

Presentation of case: A 34-year-old man developed a mass beneath the left nipple over 2 years. Although the mass was painless, it gradually enlarged over time and was accompanied by nipple discharge. Complete excision of the mass revealed that the tumor cells were arranged in solid nodule-like structures composed of clear cells and few cells with eosinophilic cytoplasm. Based on the results of immunohistochemical staining and MAML2 rearrangement analysis, a pathological diagnosis of breast CCH was made. The patient was followed up postoperatively for six months, during which there was no recurrence.

Discussion: Breast CCH differentiates from low-grade mucoepidermoid, glycogen-rich, and lipid-rich breast carcinomas. A more comprehensive understanding of breast CCH can aid pathologists in avoiding misdiagnoses during fine-needle aspiration biopsy and intraoperative frozen section diagnosis. Diagnostic clues for CCH include: (1) the presence of two types of cell morphology in the tumor, (2) immunohistochemical staining indicating p63 positivity, (3) negativity for myoepithelial markers, and (4) MAML2 gene rearrangement in certain cases.

Conclusion: The case we reported occurred in a male patient with MAML2 gene rearrangement, which is extremely rare. Complete surgical excision with adequate safety margins is the primary treatment method for breast CCH, and close postoperative follow-up should be conducted to monitor disease recurrence.