Abstract
BACKGROUND: Hyponatremia is an electrolyte abnormality that is often caused by the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and frequently encountered in the field of oncology. Although SIADH is a known complication of certain chemotherapeutic agents, its occurrence with oxaliplatin is rare. We report a case of SIADH in a patient with colon cancer who was undergoing treatment comprising capecitabine and oxaliplatin (CAPOX) plus bevacizumab. CASE PRESENTATION: A 70-year-old man with stage cT4bN2M0 colon cancer underwent chemotherapy with CAPOX plus bevacizumab. On day 7 of treatment, the patient developed severe hyponatremia (serum sodium level, 108 mmol/L) accompanied by nausea and ileus. Laboratory test results were consistent with SIADH, including low serum osmolality, elevated urine osmolality, elevated sodium concentration, and elevated antidiuretic hormone levels. The condition improved with 3% saline infusion and fluid restriction. No other underlying causes, such as central nervous system lesions or adrenal or thyroid dysfunction, were identified. CAPOX-induced SIADH was diagnosed based on clinical findings and the exclusion of other etiologies. Transition to second-line therapy was performed without SIADH recurrence. CONCLUSIONS: Oxaliplatin-based regimens may rarely induce SIADH. Clinicians should be vigilant of electrolyte disturbances during chemotherapy and promptly manage hyponatremia to avoid severe complications.