Benign spindle cell tumor not otherwise specified (NOS) in a male breast

Breast spindle cell tumors (BSCTs), although uncommon, constitute a heterogeneous group of benign and malignant lesions, often necessitating different therapeutic approaches. This study describes the case of a 62-year-old man who displayed a gradually growing retroareolar tumor of the left breast. The mass was well circumscribed, unilateral, and grossly nodular. The patient eventually underwent wide local excision of the mass. The lesion was made up of spindle cells arranged in fascicular clusters, separated by bands of collagen. No mitotic figures were observed. Immunohistochemically, the mass expressed strong and diffuse cytoplasmic staining for vimentin, CD34, CD10, and bcl-2, whereas it was negative for cytokeratins, smooth muscle actin, desmin, S-100 protein, p53, Ki-67, estrogen and progesterone receptors. Diverse histological results and immunohistochemical features established the diagnosis of benign BSCT, not otherwise specified. The patient remains disease-free 12 months after lumpectomy. This case report adds to the spectrum of the benign BSCTs and delineates the nature of different types of these lesions, in order to carefully select optimal therapeutic regimes.