Early BCa: neoadjuvant metformin fails in underpowered Spanish METTEN study

  • Martin-Castillo B & al.
  • Oncotarget
  • 2 Nov 2018

  • curated by Miriam Davis, PhD
  • Univadis Clinical Summaries
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Takeaway

  • Adding antidiabetic doses of metformin to neoadjuvant trastuzumab+chemotherapy failed to significantly improve the pathologic complete response (pCR) rate or reduce the need for mastectomy in the phase 2 METTEN trial of human epidermal growth factor receptor 2 (HER2)-positive early breast cancer (eBCa).
  • Because the study was underpowered, findings should be interpreted with caution.

Why this matters

  • Findings are consistent with previous observational studies and warrant progression to a phase 3 trial.

Study design

  • Phase 2 trial of patients randomly assigned to 12 cycles of weekly paclitaxel plus trastuzumab, followed by four cycles of FE75C (fluorouracil, epirubicin, and cyclophosphamide) administered every 3 weeks either plus trastuzumab with metformin (850 mg twice daily; n=38) or without (n=41); all patients subsequently underwent mastectomy or breast-conserving surgery [BCS]).
  • Primary outcome: pCR rate in the per protocol population.
  • Funding: Ministerio de Sanidad, Servicios Sociales e Igualdad.

Key results

  • Metformin was associated with a numerically but nonsignificantly higher pCR rate (65.5% vs 58.6% in the control group; OR, 1.34; P=.589).
  • Metformin was tied to a numerically but nonsignificantly higher rate of BCS (79.3% vs 58.6%; P=.089).
  • Metformin-treated patients had a 13% dropout rate because of gastrointestinal symptoms.

Limitations

  • Small size.
  • Open-label design.

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