Background: Apocrine cells are a common finding in female mammary cysts, while only rare cases of apocrine metaplasia in gynecomastia have been found in surgical specimens.
Case: A 65-year-old male presented with painful, monolateral gynecomastia. Fine needle aspiration biopsy showed sheets of large, eosinophilic epithelial cells. On immunocytochemistry these cells were positive for apocrine marker GCDFP-15. The patient had ischemic heart disease and was under treatment with spironolactone.
Conclusion: Apocrine cysts in gynecomastia are rare histologic findings, and this is the first case diagnosed by fine needle aspiration. The finding of apocrine cells confirms the nonneoplastic nature of the lesion, avoiding surgical excision.