Two cases of SIADH in patients with gastrointestinal cancer possibly induced by CDDP in FP chemotherapy

Case 1: A 68-year-old woman with esophageal cancer (stage IV) was treated with FP chemotherapy (5-FU at 750 mg/day for 5 days + CDDP at 80 mg/day for 1 day). On day 5 of administration, she suffered a consciousness disorder, convulsions, and hyponatremia (109 mEq/L), and was diagnosed with inappropriate secretion of antidiuretic hormone (SIADH). Case 2: A 60-year-old woman with pancreatic head cancer (stage IV_A) was treated with FP chemotherapy (5-FU at 250 mg/day by continuous arterial infusion + CDDP at 10 mg third a week by arterial infusion). After the fourth cycle of chemotherapy, she suffered myelosuppression (Grade 4) and hyponatremia (123 mEq/L). Judging from urine Na of 125 mEq/L, 24-hour urine Na of 525 mEq/day, and serum ADH of 7.9 pg/mL, she was diagnosed with SIADH. Frequent measurement of serum Na appears to be useful for the early detection and treatment of SIADH. These are, to our knowledge, the first cases of SIADH reported in patients with gastrointestinal solid cancer apparently induced by CDDP.