- Fluoropyrimidine-based S-1 added to endocrine therapy in postoperative adjuvant treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2 (HER2)-negative breast cancer yields DFS benefit.
- Invasive DFS (iDFS) increased, as did 5-year estimates in this phase 3 trial.
Why this matters
- Persistent recurrence risk with this most common breast cancer requires therapies to complement endocrine-based approaches.
- S-1 is a 5-fluorouracil prodrug that inhibits proliferation, combined with a booster (gimeracil) and oteracil to combat gastrointestinal toxicity.
- Open-label, phase 3 randomized POTENT trial of 1939 intermediate-/high-risk Japanese patients with stage I-III HR+, HER2-negative breast cancer, received endocrine therapy with or without fluoropyrimidine-based S-1.
- Funding: Comprehensive Support Project; Public Health Research Foundation; Taiho Pharmaceutical.
- Median follow-up: 51.4 months.
- Recurrence seen in 101 of 957 (10.6%) on treatment vs 155 of 973 (15.9%) in the control group.
- Estimated 5-year iDFS was 86.9% with add-on S-1 vs 81.6% without S-1.
- For treatment vs control, the HR for iDFS was 0.63 (P<.001>
- The treatment group experienced significantly more grade ≥3 neutrophil decreases and diarrhea (both P<.0001>
- Included only patients in Japan.
- Results presented without peer review.
- Study investigator Dr Masakazu Toi, professor of breast surgery at Kyoto University Hospital in Japan, where the trial was conducted said the safety profile is “manageable”.