April 2022: Adjuvant pertuzumab significantly improved invasive disease-free survival for HER2-positive, N-positive early breast cancer in the APHINITY trial

The primary analysis of the randomized, phase 3 APHINITY (NCT01358877) trial showed that one year of adjuvant pertuzumab added to trastuzumab and chemotherapy statistically significantly improved invasive disease-free survival (iDFS) compared with placebo added to trastuzumab and chemotherapy overall and for patients with node (N)-positive disease (von Minckwitz et al. N Engl J Med 2017). This study investigated whether adding pertuzumab could benefit some N-negative subpopulations and whether to consider de-escalation for some N-positive subpopulations using Subpopulation Treatment Effect Pattern Plot (STEPP) analyses.

Highlights:

• Pertuzumab significantly improved invasive iDFS for HER2-positive early breast cancer in APHINITY.
• Benefit was seen overall and for N-positive cohort, but not for N-negative disease.
• STEPP explored pertuzumab benefit size for tumor burden and biologic factor subpopulations.
• For N-negative cohort, no subpopulation with a pertuzumab benefit was identified.
• For N-positive patients, all benefited; largest gain for high tumor infiltrating lymphocytes (TILs), low risk and median HER2 copy number.

Conclusion: STEPP plots for N-negative cohort did not identify subpopulations clearly benefiting from adding pertuzumab, and those for N-positive cohort did not identify subpopulations warranting de-escalation. TILs percentage appeared to be more predictive of pertuzumab treatment effect than clinical composite risk score.

Gelber RD, Wang XV, Cole BF, et al. Six-year absolute invasive disease-free survival benefit of adding adjuvant pertuzumab to trastuzumab and chemotherapy for patients with early HER2-positive breast cancer: A Subpopulation Treatment Effect Pattern Plot (STEPP) analysis of the APHINITY (BIG 4-11) trial. Eur J Cancer. 2022 May;166:219-228. doi: 10.1016/j.ejca.2022.01.031.

• PubMed Link: https://pubmed.ncbi.nlm.nih.gov/35313167/