Pulmonary pleomorphic carcinoma with multiple metastases to the right posterior knee complicated by paraneoplastic hypercalcemia.

In this report, we describe the case of a 46-year-old male who presented with a three-month history of progressive intermittent pain over the right posterior knee. Magnetic resonance imaging showed soft tissue masses over the right popliteal fossa. Surgery was performed, and histological examination revealed the mass to be a sarcomatoid carcinoma of poor differentiation. Fluorodeoxyglucose (FDG)-positron emission tomography showed FDG uptake in the lungs and in the right para-aortic and popliteal regions. On the basis of the morphological and immunohistochemical features of the specimens, the patient's condition was diagnosed as a pulmonary pleomorphic carcinoma with multiple metastases. Systemic chemotherapy was initiated with paclitaxel and cisplatin. The patient then developed paraneoplastic hypercalcemia and ultimately succumbed to healthcare-acquired pneumonia. The results of this rare case indicate that pulmonary pleomorphic carcinomas respond poorly to combination chemotherapy with paclitaxel and cisplatin. The firm mass in the popliteal fossa that was situated behind the knee was considered to be a Baker cyst; however, the possibility of malignant metastatic sarcomas, such as pulmonary sarcomatoid carcinoma, should be considered in the differential diagnosis. In conclusion, we emphasize that pretherapeutic examinations should be the basis for the diagnosis of a mass lesion at either an unusual or usual site.