Malignant sweat gland tumor of breast arising in pre-existing benign tumor: A case report

BACKGROUND: Sweat glands belong to skin appendages. Sweat gland tumors are uncommon, especially when they occur as malignant tumors in the breast. We report a case of malignant sweat gland tumor of the breast, including imaging and pathological findings. CASE SUMMARY: A 47-year-old woman visited our hospital with a non-tender palpable lesion in her left breast. The lesion had not shown changes for 10 years. However, it recently increased in size. Sonography showed a well circumscribed cystic lesion with internal debris and fluid-fluid level. Magnetic resonance imaging showed a well circumscribed oval mass with T1 hyper-intensity compared to muscle and T2 high signal intensity. There was a small enhancing mural component in the inner wall of the mass. The tumor was resected. Its pathologic result was a malignant transformation of benign sweat gland tumor such as hidradenoma. The lesion was treated with excision and radiation therapy. At 1-year follow up, there was no local recurrence or metastasis in the patient. CONCLUSION: In the case of a rapid growing cystic mass in the nipple and subareola, it is necessary to distinguish it from a malignant sweat gland tumor.