Granular Cell Tumor of the Breast: A Case Report and a Brief Review of the Literature

Granular cell tumor (GCT) of the breast is a rare, typically benign neoplasm of Schwann cell origin, which frequently presents a significant diagnostic challenge due to its ability to clinically and radiologically mimic invasive breast carcinoma. We present the case of a 45-year-old female who presented with a palpable, firm, non-mobile mass in the right upper inner quadrant of her breast. Diagnostic imaging was highly suspicious for malignancy, with mammography revealing a high-density, spiculated, irregular mass with architectural distortion (BI-RADS 5), and ultrasound demonstrating an irregular, hypoechoic mass with severe posterior acoustic shadowing and a "taller-than-wide" orientation. Core needle biopsy was performed due to the high suspicion of malignancy. Histopathological examination revealed nests and sheets of large, polygonal cells with abundant granular, eosinophilic cytoplasm. Immunohistochemistry (IHC) studies were critical for definitive diagnosis, showing strong positivity for S100 protein and SOX10, and granular positivity for CD68, while being negative for cytokeratin markers (AE1/AE3, CAM 5.2). This immunoprofiling confirmed the diagnosis of benign GCT. The patient was successfully treated with complete surgical excision (R0 resection) and has remained free of local recurrence at three years of follow-up. This case underscores the critical role of tissue diagnosis and characteristic IHC in differentiating this rare benign entity from malignant breast lesions, thereby preventing unnecessary aggressive treatment.