Abstract
A 73-year-old man presented to our hospital with pharyngeal pain. After CT, PET, and MRI examinations and endoscopy, he was diagnosed with laryngeal cancer (cT2N0M0). He was treated with CRT combined with CDDP (80mg/m2). The tumor response was good, but due to adverse events, which include hyponatremia (Grade 3), leukocytopenia (Grade 3) and an increased creatinine level (Grade 2；creatinine clearance rate < 60 mℓ/min), we used S-1 for the rest of the patient's radiation therapy. After the administration of S-1, severe adverse events occurred, including diarrhea (Grade 4), myelosuppression (Grade 4), Hyponatremia (Grade 4), and DIC (Grade 3). We immediately ceased the administration of S-1；however, he took 2 months to recover. We considered that congenital DPD partial deficiency caused the development of these adverse events；however, we were unable to diagnose his condition because his DHU and URA levels were within the normal ranges.
