SABCS 2019 – Adding S-1 to endocrine treatment improves survival in HR+, HER2− breast cancer


  • Ben Gallarda
  • Univadis
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Takeaway

  • 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.

Study design

  • 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.

Key results

  • 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>

Limitations

  • Included only patients in Japan.
  • Results presented without peer review.

Expert commentary

  • 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”.