S-1 + oxaliplatin + 5-fluorouracil + leucovorin calcium

S-1 + oxaliplatin + 5-fluorouracil + leucovorin calcium is a multi-agent chemotherapy regimen used primarily in the treatment of gastrointestinal cancers, including advanced gastric and colorectal cancer. This combination brings together four agents with complementary mechanisms: - **S-1** is an oral fluoropyrimidine derivative that combines tegafur (a prodrug of fluorouracil), gimeracil (an inhibitor of dihydropyrimidine dehydrogenase to increase 5-FU bioavailability), and potassium oteracil (to reduce gastrointestinal toxicity). S-1 acts as a prodrug for 5-fluorouracil, providing continuous exposure to the active drug[3]. - **Oxaliplatin** is a platinum-based chemotherapeutic that forms DNA crosslinks, inhibiting DNA replication and transcription. - **5-Fluorouracil (5-FU)** is an antimetabolite that inhibits thymidylate synthase, disrupting DNA synthesis. - **Leucovorin calcium** enhances the binding of 5-FU to thymidylate synthase, increasing its cytotoxicity. This regimen may be referred to as SOX plus infusional 5-FU/leucovorin or as an extended FOLFOX variant with S-1 substitution or addition. It has been studied in perioperative settings for locally advanced gastric cancer and in metastatic colorectal cancer. The combination leverages both oral and intravenous administration routes for optimal efficacy[3][7].