A case of granular cell tumor of the breast in a 43-year-old woman is described. The patient presented with a painless mass in the upper-outer quadrant of her right breast. Mammography showed a spiculated tumor and ultrasonography demonstrated a hypoechoic mass with an irregular border. Magnetic resonance (MR) mammography revealed a homogeneous enhanced mass in Tl-weighted images using Gd-DTPA and a ringed high-intensity area around the mass in T2-weighted images. Fine-needle aspiration cytology failed to show any malignant cells. A partial resection of the breast was performed and histological examination revealed a granular cell tumor.

Granular cell tumors are generally always benign, but they may be misdiagnosed as malignant tumors because of their mammographic and ultrasonographic findings. MR mammography did not reveal a typical breast cancer in either Tl- or T2-weighted images in the present case. This case illustrates the need for care in preoperative examinations in order to avoid overdiagnosis of breast cancer.