Pulmonary Carcinosarcoma Imitating Teratocarcinosarcoma: A Case Report.

Pulmonary carcinosarcoma is a rare tumor composed of non-small-cell carcinomas and sarcomatous elements, which is poorly differentiated in most cases. We present a case of carcinosarcoma with a well-differentiated carcinomatous component that required a differential diagnosis from tumors derived from teratomas, such as teratocarcinosarcoma. We present a case of a 68-year-old man who visited our hospital for an examination of a 22-mm lung tumor. The patient underwent left S1+2 segmentectomy, and his postoperative course was uneventful. No recurrence was observed in the 21-month postoperative follow-up period. The segmentectomy specimen revealed a yellow-white, well-circumscribed mass. The tumor consisted of well-differentiated squamous and glandular epithelia, and sarcomatous components of immature spindle cells, chondrosarcoma, and rhabdomyosarcoma. The patient was diagnosed with carcinosarcoma. This case included well-differentiated carcinomatous components, and it was necessary to differentiate it from teratocarcinosarcomas. There was no neural component, and without SMARCA4 loss, which is observed in teratocarcinosarcoma, and ruled out teratocarcinosarcoma. Carcinosarcomas are characterized by a biphasic histopathological pattern, making it difficult to accurately diagnose them on biopsy, which only captures a portion of the tumor. The possibility of carcinosarcoma should be considered even when the tumors derived from teratomas are suspected on preoperative biopsy.