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

•Pertuzumab (P) significantly improved invasive disease-free survival for HER2+ early breast cancer in APHINITY.•Benefit was seen overall and for node (N)+ cohort, but not for N− disease.•Subpopulation Treatment Effect Pattern Plot explored P benefit size for tumour burden and biologic factor subpopulations.•For N− cohort, no subpopulation with a P benefit was identified.•For N+, all benefited; largest gain for high tumour infiltrating lymphocytes, low risk and median HER2 copy no.