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The APHINITY trial showed that adding adjuvant pertuzumab (P) to trastuzumab and chemotherapy, compared with adding placebo (Pla), significantly improved invasive disease-free survival (IDFS) for patients with HER2+ early breast cancer both overall and for the node-positive (N+) cohort. We explored whether adding P could benefit some N− subpopulations and whether to consider de-escalation for some N+ subpopulations. Subpopulation Treatment Effect Pattern Plot (STEPP) is an exploratory, graphical method that plots estimates of treatment effect for overlapping patient subpopulations defined by a covariate of interest. We used STEPP to estimate Kaplan–Meier differences in 6-year IDFS percentages (P minus Pla: Δ ± standard error [SE]), both overall and by nodal status, for overlapping subpopulations defined by (1) a clinical composite risk score, (2) tumour infiltrating lymphocytes (TILs) percentage, and (3) human epidermal growth factor receptor 2 (HER2) FISH copy number. Because of multiplicity, a Δ of at least three SE is required to warrant attention. The average absolute gains in 6-year IDFS percentages were 2.8 ± 0.9 overall; 4.5 ± 1.2 for N+ and 0.1 ± 1.1 for N−. Largest gains were for patients with intermediate clinical composite risk (5.3 ± 1.9 overall; 6.9 ± 2.3 N+; 4.0 ± 3.0 N−), highest TILs percentage (6.3 ± 1.7 overall; 7.4 ± 2.4 N+; 3.2 ± 1.7 N−), and intermediate HER2 copy number (2.8 ± 1.9 overall; 7.4 ± 2.5 N+; −1.3 ± 1.9 N−), but clear evidence indicating a pattern of differential subpopulation treatment effects was lacking. STEPP plots for N− did not identify subpopulations clearly benefiting from adding P, and those for N+ did not identify subpopulations warranting de-escalation. TILs percentage appeared to be more predictive of P treatment effect than clinical composite risk score. clinicaltrials.gov Identifier NCT01358877. • 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. [ABSTRACT FROM AUTHOR]

Objective: The APHINITY trial assessed the effectiveness and the safety of adding pertuzumab to trastuzumab and chemotherapy (THP) compared to trastuzumab and chemotherapy (TH) in the adjuvant management of human epidermal growth factor 2-positive (HER2+) breast cancer. We performed a study to project the potential cost-effectiveness of THP vs. TH.Study Design: Trial-based cost-utility modeling analysis.Methods: We performed an economic evaluation from a payer perspective using a Markov model with six health states: invasive disease-free survival, non-metastatic recurrence, remission, first-line metastatic, subsequent line metastatic, and death. We parameterized the model using data from both arms in APHINITY extrapolated to a patient's lifetime horizon. Estimates of health state utilities were based on EQ-5D trial data and the literature, and costs were estimated from government sources and the published literature. The primary outcomes of the model were life-years (LYs), quality-adjusted LYs (QALYs), costs, and incremental cost-effectiveness ratios (ICERs). Uncertainty was addressed via univariate and probabilistic sensitivity analyses.Results: For the intention-to-treat population, the model projected improved outcomes (by 0.50 LYs and 0.45 QALYs) and increased costs (by $74 420) for ICERs of $147 774/LY gained and $167 185/QALY gained for PHT vs. HT patients. In the node-positive patient population, the model projected improved outcomes (by 0.86 LYs and 0.76 QALYs) and increased costs (by $66 647) for ICERs of $77 684/LY gained and $87 929/QALY gained. For the hormone-receptor-negative patient population, the model projected health gains, increased costs, and ICERs of $147 022/LY gained and $166 518/QALY gained. The results were sensitive to changes in the model time horizon.Conclusion: The addition of pertuzumab to the available regimens for HER2+ early breast cancer is likely to be cost-effective for patients in the U.S. at high risk of recurrence. [ABSTRACT FROM AUTHOR]