Abstract PD1-11: Mature survival update of the double-blind placebo-controlled randomised phase II PAKT trial of first-line capivasertib plus paclitaxel for metastatic triple-negative breast cancer
Authors: Schmid Peter , Abraham Jacinta , Chan Stephen , Brunt Adrian Murray , Nemsadze Gia , Baird Richard D , Park Yeon Hee , Hall Peter , Perren Timothy , Stein Robert C , Mangel László , Ferrero Jean-Marc , Phillips Melissa , Conibear John , Cortes Javier , Foxley Andrew , de Bruin Elza , McEwen Robert , Nikolaou Myria , Stetson Daniel , Dougherty Brian , Prendergast Aaron , McLaughlin-Callan Max , Burgess Matthew , Lawrence Cheryl , Cartwright Hayley , Mousa Kelly , Turner Nicholas , Wheatley Duncan 
Published: February 2021

Background: In the PAKT study, addition of the oral AKT inhibitor capivasertib to 1st-line paclitaxel therapy for metastatic TNBC resulted in significantly longer progression-free survival (PFS; primary endpoint; Schmid, J Clin Oncol 2020). The stratified PFS hazard ratio was 0.74 (95% CI, 0.50-1.08; one-sided P=0.06; predefined significance level of 0.10, one-sided; median PFS 5.9 vs 4.2 months with capivasertib vs placebo). Overall survival (OS) results were immature at the primary analysis with 53% of events but suggested long OS with capivasertib (HR, 0.61; 95% CI, 0.37-0.99; two-sided P=0.04). Here we report final results.

Methods: This double-blind, placebo-controlled, randomised phase II trial, recruited women with untreated, metastatic TNBC. Total of 140 patients were randomly assigned (1:1) to paclitaxel 90mg/m2 (days 1, 8, 15) with either capivasertib (400mg twice daily) or placebo (days 2-5, 9-12, 16-19) every 28 days until disease progression or unacceptable toxicity. The primary endpoint was PFS. Secondary endpoints included OS in the ITT population and in patients with and without PIK3CA/AKT1/PTEN-alterations.

Results: With a median F/U of 40.0 months, median OS was longer in the capivasertib arm (19.1 vs 13.5 months, stratified HR 0.70, 95% CI 0.47-1.05, p=0.085). In contrast to the earlier analysis, no meaningful differences were seen in terms of benefit with capivasertib between patients with or without alterations of PIK3CA/AKT1/PTEN. Median OS numerically favoured capivasertib vs placebo both in the PIK3CA/AKT1/PTEN-altered (stratified HR 0.58, 95% CI 0.21-1.58, p=0.290) and PIK3CA/AKT1/PTEN non-altered subgroup (stratified HR 0.74, 95% CI 0.47-1.18, p=0.207). The safety profile of capivasertib plus paclitaxel was unchanged.

Conclusions: Final OS results show a numerical trend favouring capivasertib; effects were observed regardless of PIK3CA/AKT1/PTEN alterations. Consistent with the previously observed PFS benefit, these findings support further evaluation of first-line Capivasertib plus paclitaxel for metastatic TNBC in the ongoing Capitello290 randomised phase III trial in patients with and without PIK3CA/AKT1/PTEN alterations.

Citation Format: Peter Schmid, Jacinta Abraham, Stephen Chan, Adrian Murray Brunt, Gia Nemsadze, Richard D Baird, Yeon Hee Park, Peter Hall, Timothy Perren, Robert C Stein, László Mangel, Jean-Marc Ferrero, Melissa Phillips, John Conibear, Javier Cortes, Andrew Foxley, Elza de Bruin, Robert McEwen, Myria Nikolaou, Daniel Stetson, Brian Dougherty, Aaron Prendergast, Max McLaughlin-Callan, Matthew Burgess, Cheryl Lawrence, Hayley Cartwright, Kelly Mousa, Nicholas Turner, Duncan Wheatley. Mature survival update of the double-blind placebo-controlled randomised phase II PAKT trial of first-line capivasertib plus paclitaxel for metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD1-11.