Granular Cell Tumor of the Breast Coexisting with Ductal Carcinoma in situ: Case Report

Granular cell tumor (GCT) is a benign tumor arising from Schwann cells. GCT of the breast is rare and while predominantly benign, it can be difficult to differentiate from breast cancer by imaging. While it is not generally associated with breast cancer, we here report a rare case of GCT coexisting with ductal carcinoma in situ (DCIS). A 38-year-old Japanese woman had microcalcification suggestive of malignancy in the right upper breast and a 6-cm well-defined mass in the right lower breast. Ultrasonography showed that the lower mass was circular in shape with a clear border, and internal echo level was slightly uneven. Contrast-enhanced magnetic resonance imaging found that the inside was unevenly contrast-enhanced and showed fast/washout enhanced pattern. Hence, imaging could not exclude malignancy. Pathological diagnosis from biopsies taken from the upper calcification and lower mass was DCIS and GCT, respectively. Imaging showed no evidence of continuity between the two, but the patient elected for mastectomy. Final pathological diagnosis confirmed an S-100-positive and keratin-negative GCT for the lower lesion and no histological evidence of continuity. Although GCT is a rare disease, greater awareness of the disease and its imaging findings is needed to avoid overdiagnosis, particularly when it coexists with breast cancer.