Malignant phyllodes tumor of breast with lung metastases mimicking the primary

We report a case of recurrent malignant phyllodes tumor with liposarcomatous transformation metastasizing to the lung. The unusual feature of this case was that the metastases reproduced the primary tumor and contained ductal structures and elements of sarcoma. The origin of the ductal structures in the lung metastases was confirmed to be from the phyllodes tumor, on the basis of their immunophenotype. The epithelial cells were positive for steroid receptors and GCDFP-15, and the myoepithelial cells were positive for anti-smooth-muscle-specific proteins. We also reevaluated by immunohistochemistry a case of phyllodes tumor previously published by West et al., allegedly containing epithelial structures of supposed breast origin within lung metastases. The epithelial component was shown to consist of entrapped alveolar lining cells: