Abstract
A 51-year-old man visited our hospital with a main complaint of precordial pain, difficulty swallowing, and pyrexia. The patient was diagnosed with esophageal carcinosarcoma, based on the characteristic morphology noted on upper gastrointestinal endoscopy and histology tests, and he underwent surgical treatment. His preoperative blood granulocyte-colony stimulating factor (G-CSF) and interleukin-6 (IL-6) levels were high, and the surgical specimens were positive in both immunohistochemical tests; therefore, he was diagnosed with a G-CSF- and IL-6-producing tumor. When pyrexia is seen as a paraneoplastic symptom, it is important to consider and investigate the possibility of a cytokine-producing tumor.