Left breast epithelioid MPNST with concurrent right breast cancer: no recurrence after surgery

What happened, in summary

This 76-year-old woman came to the hospital after noticing enlarging masses in both breasts over the previous year. She had no family history of breast, ovarian, pancreatic, or prostate cancer and no clinical signs of neurofibromatosis, such as café-au-lait spots, Lisch nodules, or cutaneous neurofibromas. On examination, the right breast mass measured 40 mm and the left breast mass measured 80 mm. Mammography, ultrasound, and breast MRI showed suspicious findings in both breasts. Biopsy of the right breast showed invasive ductal carcinoma that was strongly hormone receptor-positive, with ER Allred score 8 and PR Allred score 8, HER2 1+ / HER2-negative status, and Ki-67 of 7%. Biopsy of the left breast showed a mesenchymal tumor. Surgery included right total mastectomy with sentinel lymph node biopsy and left total mastectomy. Final pathology showed 2 different cancers. The right breast had a 50 × 42 × 60 mm invasive ductal carcinoma, staged pT3N0M0, Stage IIB. The left breast had a 75 × 70 × 60 mm epithelioid malignant peripheral nerve sheath tumor, an uncommon tumor type in the breast. The left tumor had spindle cells, epithelial-like cells, and mild invasion of surrounding mammary tissue. Immunohistochemistry was positive for vimentin, S100, and SOX10, with partial cytokeratin AE1/AE3 positivity and maintained H3K27me3 expression. These markers helped confirm that the left-sided tumor was biologically different from the right-sided ductal cancer. It was staged pT2, Stage IIIA, histological malignancy grade 2. After surgery, she received oral anastrozole for the right breast cancer. No adjuvant therapy was given for the left epithelioid MPNST. As of March 2025, 3 years after surgery, neither tumor had recurred.