Epithelioid Malignant Peripheral Nerve Sheath Tumor of the Breast with Breast Cancer in the Contralateral Breast: A Case Report.

INTRODUCTION

Malignant peripheral nerve sheath tumors (MPNSTs) are common in the peripheral nerves of the head, neck, and limbs, with few reports of their occurrence in the breasts, and the epithelioid type is rare. Here, we aimed to report a case of an epithelioid MPNST of the breast.

CASE PRESENTATION

A 76-year-old woman presented with bilateral breast masses. Pathological findings showed a 60-mm invasive ductal carcinoma (T3N0M0 stage IIB) on the right breast and an epithelioid MPNST on the left breast. After surgical resection, the patient was treated with endocrine therapy alone for right breast cancer, and no recurrence was observed 4 years after surgery.

CONCLUSION

Reports of MPNSTs in the breasts are rare. The pathological analysis showed atypia of spindle cells, positive staining for vimentin, S100, SOX10, and epithelial-like cells, and positive staining for cytokeratin AE1/AE3. H3K27me3 is reportedly absent in typical MPNSTs; however, it is expressed in epithelioid types. It sometimes occurs in patients with a germline mutation in , where INI1 is absent in tumor cells. In this case, the tumor cells expressed H3K27me3 and also maintained INI1.