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

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.

Capivasertib Plus Paclitaxel Versus Placebo Plus Paclitaxel As First-Line Therapy for Metastatic Triple-Negative Breast Cancer: The PAKT Trial

PURPOSE

The phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway is frequently activated in triple-negative breast cancer (TNBC). The AKT inhibitor capivasertib has shown preclinical activity in TNBC models, and drug sensitivity has been associated with activation of PI3K or AKT and/or deletions of PTEN. The PAKT trial was designed to evaluate the safety and efficacy of adding capivasertib to paclitaxel as first-line therapy for TNBC.

PATIENTS AND METHODS

This double-blind, placebo-controlled, randomized phase II trial recruited women with untreated metastatic TNBC. A total of 140 patients were randomly assigned (1:1) to paclitaxel 90 mg/m² (days 1, 8, 15) with either capivasertib (400 mg twice daily) or placebo (days 2-5, 9-12, 16-19) every 28 days until disease progression or unacceptable toxicity. The primary end point was progression-free survival (PFS). Secondary end points included overall survival (OS), PFS and OS in the subgroup with PIK3CA/AKT1/PTEN alterations, tumor response, and safety.

RESULTS

Median PFS was 5.9 months with capivasertib plus paclitaxel and 4.2 months with placebo plus paclitaxel (hazard ratio [HR], 0.74; 95% CI, 0.50 to 1.08; 1-sided P = .06 [predefined significance level, 1-sided P = .10]). Median OS was 19.1 months with capivasertib plus paclitaxel and 12.6 months with placebo plus paclitaxel (HR, 0.61; 95% CI, 0.37 to 0.99; 2-sided P = .04). In patients with PIK3CA/AKT1/PTEN-altered tumors (n = 28), median PFS was 9.3 months with capivasertib plus paclitaxel and 3.7 months with placebo plus paclitaxel (HR, 0.30; 95% CI, 0.11 to 0.79; 2-sided P = .01). The most common grade ≥ 3 adverse events in those treated with capivasertib plus paclitaxel versus placebo plus paclitaxel, respectively, were diarrhea (13% v 1%), infection (4% v 1%), neutropenia (3% v 3%), rash (4% v 0%), and fatigue (4% v 0%).

CONCLUSION

Addition of the AKT inhibitor capivasertib to first-line paclitaxel therapy for TNBC resulted in significantly longer PFS and OS. Benefits were more pronounced in patients with PIK3CA/AKT1/PTEN-altered tumors. Capivasertib warrants further investigation for treatment of TNBC.