What happened, in summary

This 46-year-old woman was referred after noticing 2 painless lumps in the upper outer quadrant of her left breast that had grown rapidly over 3 weeks. On examination, the masses were firm, mobile, and close together, measuring about 4.0 × 4.0 cm and 3.0 × 3.0 cm. There were no skin changes, nipple changes, palpable axillary nodes, or abnormal findings in the opposite breast. Mammography showed 2 well-circumscribed high-density masses with heterogeneous microcalcifications, while ultrasound showed a larger complex lesion. She underwent modified radical mastectomy with axillary lymph node dissection. Gross examination showed a cystic-solid tumor with 2 parts, measuring 7.0 cm in length and width and 5.0 cm in height, with intracystic hemorrhage. Microscopy showed mixed epithelial and mesenchymal metaplastic carcinoma, also called carcinosarcoma, histologic grade III. No metastasis was found in 15 lymph nodes. Biomarker staining differed by tumor component. The epithelial component was ER-positive, PR-positive, and C-erbB-2/HER2-positive. The mesenchymal component was ER-negative, PR-negative, and weakly C-erbB-2/HER2-positive. Ki-67 was 20%. Other staining showed vimentin, SMA, and CD68 positivity, with CK, CK5/6, CK7, desmin, S-100, and CD34 negativity. Because the tumor was rare and mixed epithelial-mesenchymal in pattern, treatment combined surgery with systemic therapy rather than relying on local excision alone. She then received 3 cycles of CEF chemotherapy, 3 cycles of Taxotere/docetaxel, and tamoxifen. As of March 2014, 1 year after surgery, she was doing well with no recurrence or metastasis. The absence of nodal disease and the clear 1-year follow-up were important because metaplastic breast carcinomas are uncommon and can behave aggressively despite variable receptor staining.