Granular Cell Tumor of the Breast Mimicking Carcinoma: A Case Highlighting Radiologic-Pathologic Discordance

Granular cell tumor (GCT) of the breast is a rare benign neoplasm of Schwann cell origin that can closely mimic breast carcinoma both clinically and radiologically, posing a significant diagnostic challenge. Core needle biopsy plays a crucial role in establishing the diagnosis. We present a case of a 72-year-old woman with a palpable right breast mass. Imaging findings were highly suspicious for malignancy, including high density on mammography and marked posterior acoustic shadowing on ultrasound. Initial core needle biopsy results were discordant with the radiological features, prompting repeat tissue sampling. The patient underwent surgical excision following preoperative injection of superparamagnetic iron oxide (SPIO) nanoparticles (Magtrace) in anticipation of a potential sentinel lymph node biopsy. Intraoperative frozen-section analysis revealed a benign lesion, allowing avoidance of sentinel lymph node biopsy. Final histopathological and immunohistochemical evaluation demonstrated polygonal cells with abundant eosinophilic granular cytoplasm and positivity for S100 and CD68, consistent with a granular cell tumor. This case highlights the importance of radiologic-pathologic correlation in breast lesions with discordant findings and underscores the role of emerging techniques, such as SPIO tracers, in enabling flexible, patient-tailored surgical management, ultimately helping to avoid overtreatment.