Efficacy and Safety of Oral 5-FU Derivatives After Progression of HR+/HER2- Metastatic Breast Cancer on CDK4/6 Inhibitor.

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.