A case report of granular cell tumor of the axillary subcutaneous tissue difficult to differentiate from metastatic breast cancer

Background : Granular cell tumors are relatively rare tumors originating from Schwann cells that can occur anywhere in the body. Herein, we report a case of granular cell tumor arising in the axillary region, which was difficult to distinguish from metastatic breast cancer.Case : A 47-year-old woman underwent partial mastectomy, sentinel lymph node biopsy, and radiation therapy for right upper outer quadrant breast cancer. After 5 years, she presented with a subcutaneous mass in the right axilla with a maximum diameter of 1.0 cm, and lymph node recurrence was suspected. Fine-needle aspiration cytology revealed a small number of spindle-shaped cells with coarse and abundant cytoplasmic granules. These cells were difficult to differentiate from apocrine metaplastic cells or apocrine carcinoma cells, but the tumor was eventually diagnosed as a granular cell tumor by core needle biopsy.Conclusion : Granular cell tumors, composed of cells containing abundant and granular cytoplasm, should be considered in the differential diagnosis of breast tumors, because they can arise in any organ of the body. Trauma associated with the surgery and radiation therapy may have contributed to the development of granular cell tumor in our patient.