S-1 as an alternative treatment after 5-fluorouracil-induced coronary vasospasm in a patient with small bowel adenocarcinoma: a case report.

5-Fluorouracil (5-FU) is a chemotherapeutic agent used worldwide to treat various solid tumors. It may cause adverse cardiotoxic events, the most common of which is coronary vasospasm. Recently, the 2022 European Society for Medical Oncology guidelines for metastatic colorectal cancer recommended S-1 as an alternative therapy after 5-FU-induced cardiotoxicity; however, only limited data on Asian patients are available.