Histogenesis of metaplastic breast carcinoma and axillary nodal metastases.

A 40-year-old breast-feeding woman presented with left breast swelling. On physical examination a 7 cm mass was found in the breast. Because biopsy demonstrated malignant tissue, mastectomy with axillary nodal dissection was performed. Pathological findings were consistent with metaplastic breast carcinoma with nodal metastases. The primary tumor consisted of three types of invasion: ductal, squamous, and sarcomatous. Furthermore, three morphological transitions were observed: ductal-squamous, ductal-sarcomatous, and squamous-sarcomatous. Ductal-squamous (12/18 microscopy slides) and squamous-sarcomatous transitions (10/18) were more commonly observed than ductal-sarcomatous transition (3/18). Furthermore, immunohistochemistry showed loss of epithelial marker (cytokeratin) and acquisition of mesenchymal markers (vimentin and alpha-smooth muscle actin) in the sarcomatous component. These findings suggested that epithelial-mesenchymal transition had occurred in the tumor and that two pathways, ductal-squamous-sarcomatous and ductal-sarcomatous transition, were involved in progression of metaplastic breast carcinoma. The main pathway appeared to be ductal-squamous-sarcomatous transition. Regarding the nodal metastases, of 13 positive nodes, ductal, squamous, and sarcomatous components were observed in 13, seven, and two nodes, respectively. Moreover, as in the primary tumor, ductal-squamous and squamous-sarcomatous transitions were observed. This suggested that the ductal component metastasized to the nodes and that epithelial-mesenchymal transition subsequently occurred within the nodes.