Malignant peripheral nerve sheath tumor (MPNST) is a rare variety of soft tissue sarcoma of ectomesenchymal origin. It represents approximately 10% of all soft tissue sarcomas. Though these tumours due to their Schwann cell origin may occur anywhere near a nerve trunk, breast is a rare site of its occurrence. This is a rare case of giant malignant peripheral nerve sheath tumor arising in the breast and not associated with neurofibromatosis type 1. A 22-year female presented with a large painless breast lump for five months, which was clinically suspected to be a Carcinoma. No confirmatory results were obtained with FNAC, Core biopsy and MRI. Wide local excision was done. Histopathology and IHC confirmed MPNST.

Keywords: Malignant Peripheral Nerve Sheath tumor, soft tissue sarcoma, breast, immunohistochemistry, Wide local excision.