[Malignant Melanoma of a Male Breast That Was Difficult to Differentiate from Breast Cancer-A Case Report].

Introduction: Malignant melanoma in the male breast is extremely rare. Here we report a case of malignant melanoma in which a small cystic lesion in the male breast gradually increased during follow-up and was difficult to distinguish from breast cancer.

Case: A 65-year-old male was diagnosed with a tumor in the right breast and was referred to our department for further examination. At 42 years of age, he underwent tumor resection of a malignant melanoma of the abdominal skin. Mammary ultrasonography showed a 0.6 cm cystic mass in his right breast. Eight months later, the right breast mass had increased to 1.4 cm, and a core needle biopsy suggested breast cancer. Total mastectomy with axillary lymph node dissection was performed. HE staining of the resected tumor showed intranuclear inclusion bodies and some large nucleoli. On the basis of various immunostaining methods, malignant melanoma was diagnosed instead of breast cancer. After surgery, adjuvant chemotherapy with molecularly targeted drugs was administered.

Discussion: This might have been a case of male breast metastasis of malignant melanoma with very late recurrence.