Granular cell tumour of the breast: An uncommon benign lesion with suspicious radiological features. Case report and literature review.

Granular cell tumour is an uncommon benign lesion of neural lineage, associated with ATP6AP1 and ATP6AP2 inactivating mutations (endosomal pH regulators). These tumours typically develop in the head and neck region, particularly in the tongue, and are rarely found in the mammary gland, with an estimated incidence of 1:1000 of all breast tumours. They have similar clinical and radiological features, that usually mimic malignant lesions with spiculated margins. Histologically, they present a characteristic morphology, which may require differential diagnosis from other granular cell entities, including benign conditions (such as histiocyte-rich inflammatory reactions) and malignant neoplasms such as the histiocytoid variant of lobular carcinoma or apocrine carcinoma. We present a case of granular cell tumour of the breast, radiologically classified as BI-RADS 5, to highlight the importance of morphological and immunohistochemical studies for establishing a definitive diagnosis.