PT  - JOURNAL ARTICLE
AU  - KOI, YUMIKO
AU  - TAJIRI, WAKAKO
AU  - KAWASAKI, JUNJI
AU  - AKIYOSHI, SAYURI
AU  - IJICHI, HIDEKI
AU  - NAKAMURA, YOSHIAKI
AU  - KOGA, CHINAMI
AU  - TOKUNAGA, ERIKO
TI  - Efficacy and Safety of Oral 5-FU Derivatives After Progression of HR<sup>+</sup>/HER2<sup>−</sup> Metastatic Breast Cancer on CDK4/6 Inhibitor
AID  - 10.21873/anticanres.17895
DP  - 2025 Dec 01
TA  - Anticancer Research
PG  - 5609--5618
VI  - 45
IP  - 12
4099  - http://ar.iiarjournals.org/content/45/12/5609.short
4100  - http://ar.iiarjournals.org/content/45/12/5609.full
SO  - Anticancer Res2025 Dec 01; 45
AB  - Background/Aim: Optimal treatment strategies following disease progression on cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) plus endocrine therapy (ET) for patients with hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2−) metastatic breast cancer (MBC) remain undefined. Oral 5-fluorouracil (5-FU) derivatives, such as tegafur/gimeracil/oteracil (S-1) and capecitabine, are widely used and offer convenience of administration. This study aimed to evaluate the efficacy and safety of oral 5-FU derivatives in such a treatment setting in patients with HR+/HER2− MBC.Patients and Methods: We retrospectively analyzed 40 patients with HR+/HER2− MBC who received oral 5-FU derivatives following progression on CDK4/6i plus ET. Clinical outcomes including time to treatment failure and adverse events were assessed.Results: Of the 40 patients, 97.5% received abemaciclib, and 95.0% were treated with S-1. The median time to treatment failure was 12.3 (range=1.2-29.2) months. Grade 3 adverse events noted were reduced neutrophil count, anemia, alanine aminotransferase increase, and generalized edema, which led to dose reduction but did not result in treatment discontinuation.Conclusion: These findings highlight the potential of oral 5-FU derivatives as effective and safe treatment options to use after progression on CDK4/6i plus ET for patients with HR+/HER2− MBC.