Metaplastic carcinoma of the breast with heterologous mesen-chymal (neuroectodermal) differentiation: a clinicopathological analysis and literature review.

A 32-year-old woman presented with a gradually enlarging left breast mass over one year. Breast magnetic resonance imaging (MRI) revealed a mass at the 9 o'clock position in the left breast, classified as BI-RADS category 6. She underwent endoscopic left breast-conserving surgery and sentinel lymph node biopsy. Histological examination (H&E staining) revealed a tumor composed of sheets of epithelioid cells and fascicles of spindle cells, with areas of transition between the two components. Epithelioid cells were small, round to short-spindled, with scant cytoplasm, crowded arrangement, and coarse chromatin. Spindle cells were loosely arranged with indistinct borders, mildly eosinophilic cytoplasm, inconspicuous nucleoli, and intervening pale pink matrix. Immuno-histochemistry (IHC) demonstrated: Epithelioid cells were diffusely positive for CK8/18 and CAM5.2; partially positive for pan-CK and CK7; focally positive for CK5/6, CK14, high molecular weight cytokeratin (HCK), and P63; diffusely positive for E-cadherin; and negative for vimentin. Spindle cells were positive for synaptophysin (Syn), CD56, glial fibrillary acidic protein (GFAP), and vimentin, but negative for epithelial markers (pan-CK, CK7, CK8/18, CAM5.2, E-cadherin). The final diagnosis was metaplastic carcinoma with heterologous mesenchymal (neuroectodermal) differentiation. Postopera-tively, the patient received 8 cycles of EC-T systemic chemotherapy. Follow-up with breast MRI and chest CT every 3 months for 23 months (1 year and 11 months) showed no evidence of tumor recurrence or metastasis.