P30-8 Sarcomatoid Changes of Pulmonary Squamous Cell Carcinoma to Pulmonary Spindle Cell Carcinoma

Pulmonary spindle cell carcinoma (PSCC) is a very rare subtype of pulmonary sarcomatoid carcinoma (PSC), which consists of spindle cells only. We report a PSCC case in an 80-year-old man with systemic multiple metastases; however, the pathological image showed a sarcoma. The patient was diagnosed with pulmonary squamous cell carcinoma (SCC) 11 years ago and underwent chemoradiation therapy (CDPP + VNR + RT). Moreover, he had prostate cancer 4 years ago and underwent endocrine radiation therapy (BCL + Leuprorelin + IMRT). No recurrence of both carcinomas has ever been observed. He was referred to our hospital due to back pain and an MRI revealed a malignant tumor in the back. A rise of tumor marker level was seen, and PET-CT scan showed systemic accumulation of FDG, including humerus, femur, and liver, but not in the lungs. We performed a biopsy of the tumor below the iliopsoas muscle. Histopathology showed that the tumor consisted of spindle cells, and the tumor cells were suggested to be separated into smooth muscle cells. The patient was diagnosed with leiomyosarcoma, and he underwent treatment with Pazopanib. However, he died 2 months after the hospitalization. An autopsy revealed SCC with a spread of 5 cm and 9 mm adenocarcinoma in the lung. The sarcomatoid tumor consisted of spindle cells only. Immunostaining was positive for vimentin while it was weakly positive for AE1/AE3, CAM5.2, and EMA. We diagnosed systemic metastases of PSCC that originated from SCC. PSC has a poor prognosis and has advanced at the time of the diagnosis. It is often diagnosed by autopsy. Genetic testing is useful to diagnose PSCC, but in a city hospital, genetic diagnosis is not always possible. It is necessary to check detailed medical history, perform a thorough physical examination, and differentiate and diagnose PSCC from other diseases based on the clinical course and pathological features, including immunostaining.