Severe hypertriglyceridemia induced by S-1: Subsequent case series of four patients and further review of the literature

Objective: We previously reported a case where S-1, containing tegafur, gimeracil, and oteracil potassium, induced severe hypertriglyceridemia. After the case, we regularly monitored serum lipid levels and surprisingly observed an additional 4 cases within 1.5 years. We here report the treatment process. Case report: At least 3 patients exhibited hyperlipidemia at baseline; in 2 of them, this was caused by previous fluoropyrimidine treatment. One patient experienced grade 4 hypertriglyceridemia, and the other 3 grade 3 hypertriglyceridemia. One patient developed temporary serum triglyceride elevation during the S-1 administration period, and the 3 experienced persistent elevation. The severity of serum triglyceride level worsened with increasing administration and peaked in cycles 2 - 6. Fenofibrate 80 - 160 mg/day and S-1 dose reduction were effective, with some significantly and others gradually decreasing to grade 0 - 1. Discussion: The summarized clinical features are as follows: (1) Severe hypertriglyceridemia tends to appear after several treatment cycles and worsens with increasing administration. (2) It tends to occur in patients with hyperlipidemia at baseline. (3) Patients previously affected with fluoropyrimidines-induced hypertriglyceridemia can experience S-1 symptoms. (4) In some cases, it might decrease after the S-1 suspension period. (5) Fibrates and S-1 dose reductions were effective. As the final fluoropyrimidine product is fluorouracil, its presence or that of its metabolizing enzymes and the genetic background of the patients might have affected the results. We should be aware of the risk of temporal and asymptomatic occurrence of S-1-induced hypertriglyceridemia for early detection with appropriate treatment.