Low‐grade malignant peripheral nerve sheath tumor: a report of the first case in the breast and literature review
To the Editor A 65-year-old woman with a positive family history for breast cancer presented with the palpable mass in the upper outer quadrant of the left breast. Ultrasonography and mammography revealed an oval, hypoechogenic, sharply demarcated mass, measuring 23 9 14 mm, classified as Bi-RADS 4 (Fig. 1A). A core needle biopsy revealed a cellular spindle cell lesion (AE1/AE3 negative) without prominent atypia and mitotic activity (B3 category, Fig. 1B). The multidisciplinary breast meeting discussed the case and recommended a wide local excision of the mass. Grossly, the 20-mm tumor was well-circumscribed, grayish-white on cut section, without necrosis and hemorrhage (Fig. 1C). Histopathologic examination revealed a well circumscribed, spindle cell neoplasm composed of the cells with mild to moderate atypia and sporadic mitotic activity (up to 5/10 hpf mitotic figures, Fig. 1D,E). An extensive immunohistochemical (IHC) examination revealed only convincing S-100 positivity in about 20% of neoplastic cells (Fig. 1F). All other markers were negative (AE1/AE3, Cam5.2, p63, GFAP, SMA, desmin, CD34, HMB-45, SOX-10) while beta-catenin retained cytoplasmic/membranous expression without nuclear positivity. Morphologic and immunohistochemical findings were consistent with a low-grade malignant peripheral nerve sheath tumor (MPNST). Due to the tumor size, clean margins, and the tumor grade, a close follow-up without further treatment of the patient was recommended (1–3). Additional clinical