Rechallenge with 5-fluorouracil in a patient who developed encephalopathy caused by 5-fluorouracil for colon cancer

We report a case involving a patient with colon cancer who underwent 5-fluorouracil (5-FU) rechallenge and maintained an oncological effect for a long period after encephalopathy caused by 5-FU. Our patient was a 61-year-old man who was diagnosed with adenocarcinoma of the ascending colon with direct liver invasion. He underwent right hemicolectomy with partial liver resection followed by adjuvant chemotherapy with modified FOLFOX6 (mFOLFOX6). Ten months after completion of mFOLFOX6, his carcinoembryonic antigen concentration increased, and ascites was revealed by computed tomography 2 months later. We started FOLFIRI, and he was taken to our hospital by ambulance because of loss of consciousness 10 days after the start of the third cycle of FOLFIRI. Laboratory investigations showed hyperammonemia and elevations of his serum creatinine and blood urea nitrogen concentrations. Brain computed tomography demonstrated no abnormalities. Transfusion of 1500 ml of crystalloid fluid resulted in gradual recovery over the next 12 h. His ammonia concentration decreased to a normal level. Twelve days after onset of the encephalopathy, we restarted FOLFIRI, but the dose of continuous 5-FU was decreased by 20 %. The patient’s carcinoembryonic antigen concentration considerably decreased from 376.5 to 19.9 ng/ml, and his ascites disappeared. Nineteen months after the resumption of FOLFIRI, he underwent 34 courses of FOLFIRI and maintained stable disease. The encephalopathy did not recur.