LAUSR

INTRODUCTION Esophageal carcinosarcoma is a rare malignancy composed of both carcinoma and sarcoma-like spindle cells. This tumor is usually diagnosed before treatment due to its unique macroscopic appearance but accurate diagnose is difficult even via biopsy if the sarcomatous component is small. Herein, we report a rare case of esophageal carcinosarcoma showing rapid growth after definitive chemoradiotherapy. PRESENTATION OF CASE A 65-year-old man was diagnosed with locally advanced esophageal squamous cell carcinoma with lymph node metastasis. Following definitive chemoradiotherapy, the primary tumor and metastatic lymph nodes were markedly reduced. However, at 14 weeks after treatment, an ulcerative lesion appeared at the site of the primary tumor and was clinically interpreted as residual cancer. The tumor rapidly grew in a short period of time and new metastatic lesions were clinically detected in the supraclavicular lymph nodes. Salvage esophagectomy was immediately performed and histopathological examination of the resected specimen revealed that the tumor was largely composed of sarcomatous spindle cells harboring the histological transition from squamous cell carcinoma. The final diagnosis was esophageal carcinosarcoma. DISCUSSION Due to its characteristics, esophageal carcinosarcoma may occasionally get diagnosed as squamous cell carcinoma by endoscopic biopsy and chemoradiotherapy be performed for latent sarcomatous components unintentionally. There are only a few reports of esophageal carcinosarcoma treated with chemoradiotherapy, with its safety and efficacy not fully verified. CONCLUSION In cases of rapidly growing tumors following chemoradiotherapy, carcinosarcoma should be considered as one of the differential diagnoses, warranting prompt surgical procedures.