Background: The APHINITY trial demonstrated that pertuzumab, when added to adjuvant trastuzumab and chemotherapy, modestly but statistically significantly improved invasive disease-free survival (IDFS) among patients with HER2-positive, operable breast cancer. From November 2011 until August 2013, 2400 patients were randomly assigned to receive pertuzumab and 2405 to receive placebo. The clinical cut off-date for the primary analysis was 19 Dec 2016 after a median follow-up of 45.4 months. In the intent-to-treat (ITT) population, the estimates of the 3-year rates of IDFS were 94.1% in the pertuzumab group and 93.2% in the placebo group (hazard ratio [HR], 0.81; 95% confidence interval [CI], 0.66 to 1.00; P=0.045). The benefit appeared more pronounced in patients with node-positive disease, with a HR of 0.77 (95% CI 0.62-0.96), and in those with hormone receptor-negative disease, where the HR was 0.76 (95% CI 0.56-1.04). Based on these results, pertuzumab in combination with trastuzumab was approved for high risk early HER2-positive breast cancer patients. The first interim analysis of OS took place at that same time. A total of 169 patients had died, with no significant treatment effect with regards to mortality found at that time. Diarrhea, grade 3 or higher, was more frequent within the pertuzumab group (9.8%) compared with the placebo group (3.7%). Heart failure, cardiac death, and cardiac dysfunction were infrequent in both treatment groups. Results: At 74.1 months of median follow-up (clinical cut-off date June 19, 2019), we now report results of the pre-planned, calendar-driven second interim OS analysis which requires a p-value of 0.0012 to reach statistical significance. Updated descriptive analyses of IDFS and cardiac safety were also performed. Fewer deaths were observed in the pertuzumab (P) arm [125 (5.2%) vs 147 (6.1%)], however statistical significance was not reached at this interim analysis. The hazard ratio for OS is 0.85 [95% CI 0.67-1.07 (p=0.17)]; 6-year OS percents are 94.8% vs 93.9% (0.9% difference).Updated IDFS results based on 508 events in the ITT population are: hazard ratio 0.76 [95% CI 0.64-0.91]; 6-year IDFS percents are 90.6% vs 87.8% (2.8% difference). Of note, the difference was due mainly to the reduction in distant (5.9% vs 7.7%) and loco-regional (1.2% vs 2.0%) BC relapses. The node-positive cohort continues to derive clear benefit from the addition of P: hazard ratio 0.72 (95% CI 0.59-0.87). The benefit in terms of 6-year IDFS percent is 4.5% [87.9% vs 83.4%].In the node-negative cohort, the IDFS hazard ratio is 1.02 (95% CI; 0.69-1.53) with 95% of patients being event-free in both arms at 6 years.With longer follow up, a treatment benefit of P is also seen in the hormone receptor (HR) positive cohort: IDFS hazard ratio for HR positive is 0.73 (95% CI 0.59 -0.92). IDFS hazard ratio for HR negative is 0.83 (95% CI 0.63 -1.10). No new cardiac safety concerns emerged. One additional primary cardiac event (heart failure) was reported in the P arm and 1 additional patient in each arm had a secondary cardiac event resulting to 18 and 8 for primary cardiac events and 65 and 68 for secondary cardiac events in the P and placebo arms, respectively. The benefit of P in HER2+ early BC is maintained, with the greatest benefit continuing to be observed in the node positive population. With longer follow-up, the benefit of P no longer appears to depend on HR status. Continued follow up of patients is very important to determine possible benefit for OS. A calendar-driven third interim OS analysis is planned in 2.5 years, and the event-driven final OS analysis is planned when 640 deaths have occurred.

Citation Format: Martine Piccart, Marion Procter, Debora Fumagalli, Evandro de Azambuja, Emma Clark, Michael S. Ewer, Eleonora Restuccia, Guy Jerusalem, Susan Dent, Linda Reaby, Hervé Bonnefoi, Ian Krop, Tsang-Wu Liu, Tadeusz Pieńkowski, Masakazu Toi, Nicolas Wilcken, Michael Andersson, Young-Hyuck Im, Ling-Ming Tseng, Hans-Joachim Lueck, Marco Colleoni, Estefania Monturus, Mihaela Sicoe, Sébastien Guillaume, José Bines, Richard Gelber, Giuseppe Viale, Christoph Thomssen. Interim overall survival analysis of APHINITY (BIG 4-11): A randomized multicenter, double-blind, placebo-controlled trial comparing chemotherapy plus trastuzumab plus pertuzumab versus chemotherapy plus trastuzumab plus placebo as adjuvant therapy in patients with operable HER2-positive early breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr GS1-04.