Metastatic metaplastic carcinoma of the breast (MCB): an uncharacteristic pattern of presentation with clinicopathologic correlation.

Metaplastic carcinoma of the breast (MCB) is a well recognized but uncommon aberrant manifestation of poorly differentiated invasive carcinoma containing both epithelial (ductal) and mesenchymal elements as well as a transitional form between them. This heterogeneous tumor characteristically contains ductal carcinoma cells mixed with areas of diverse morphologic phenotype displaying spindle, squamous, chondroid, or osseous differentiation. Some studies have suggested that certain types of metaplastic carcinoma have a more favorable prognosis as compared with others. We describe a case involving a 67-yr-old woman who presented with metastatic nodules in the lungs and a vague but recent history of breast cancer. The case highlights a subtype of MCB with a predominant spindle cell component metastatic to the lung. Fine-needle aspiration biopsy (FNAB) smears of the nodules revealed a bland, spindle cell, mesenchymal proliferation with minimal evidence of an epithelial component. A second primary was clinically excluded and a request for review of the original slides identified a metaplastic component to the original tumor with a histologic and immunohistochemical profile identical to the metastatic tumor, confirming origin from the breast. Metaplastic carcinomas of the breast commonly bypass axillary lymph nodes and present as distant metastases. FNAB diagnosis of metaplastic carcinoma of the breast is quite difficult at the primary site and poses a formidable diagnostic challenge at a metastatic site, especially when the dominant pattern is not of the usual type. The literature is reviewed, confirming the rarity of such a presentation and the novelty of this case. Confirmation by FNAB is also quite difficult but may become more commonplace as a trend toward minimal intervention continues to gain popularity. This case emphasizes the importance of recognizing and reporting metaplastic elements in primary breast tumors, as well as the value of direct morphologic comparison of cytologic material from FNABs with archival histologic material. In such situations, the importance of complete and accurate clinicopathologic information is underscored.