Metaplastic breast carcinoma metastatic to the lung mimicking a primary chondroid lesion: Report of a case with cytohistologic correlation

This case study illustrates the unusual morphologic findings of a metastatic breast carcinoma to the lung. The tumor showed chondromatous differentiation and mimicked a primary chondroid lesion of the lung on fine-needle aspiration and needle core biopsy. The patient was a 59-year-old woman with a previous history of stage II carcinoma of the breast, which had been reported as "poorly differentiated, infiltrating ductal carcinoma," with two of 13 axillary lymph nodes showing metastatic ductal carcinoma. The pathology report received from the outside institution contained no mention of metaplastic components, and because the new pulmonary lesion was a peripherally located, well-circumscribed mass found incidentally on abdominal computed tomography scan in the lower lung field cuts, pulmonary chondroid hamartoma was initially postulated as a preliminary diagnosis. However, on review of the outside glass slide material from a prior lumpectomy, chondromatous differentiation was identified and a final diagnosis of metaplastic carcinoma of the breast with pulmonary metastasis was made. To the best of our knowledge, this is the only reported case of a metastasis of metaplastic breast carcinoma initially identified from fine-needle aspiration biopsy. The importance of recognizing and reporting metaplastic elements in primary breast tumors is discussed, and the value of direct morphologic comparison of cytologic material to prior histology is emphasized.