Capivasertib plus paclitaxel as first-line treatment for metastatic triple-negative breast cancer: results from the randomised, global phase III CAPItello-290 trial

BACKGROUND: Adding the pan-Akt serine/threonine kinase (AKT) inhibitor capivasertib to first-line paclitaxel in metastatic triple-negative breast cancer (TNBC) led to significantly longer progression-free survival (PFS) and overall survival (OS) versus placebo-paclitaxel in the phase II PAKT trial. CAPItello-290 was designed to further assess capivasertib-paclitaxel, including in patients with PIK3CA/AKT1/PTEN-altered tumours. PATIENTS AND METHODS: [day 1, weeks 1-3 (4-week cycle)] plus capivasertib 400 mg or placebo twice daily (days 2-5, weeks 1-3). PIK3CA/AKT1/PTEN alterations were analysed by retrospective central molecular testing. Dual primary endpoints were OS in the overall population and in patients with PIK3CA/AKT1/PTEN-altered tumours; investigator-assessed PFS was a key secondary endpoint. RESULTS: From July 2019 to February 2022, 812 patients were randomised; 30.7% of patients had PIK3CA/AKT1/PTEN tumour alterations. At final analysis [data cut-off (DCO) 18 March 2024], the median OS for the overall population was 17.7 and 18.0 months with capivasertib-paclitaxel and placebo-paclitaxel, respectively [hazard ratio (HR) 0.92, 95% confidence interval (CI) 0.78-1.08, P = 0.3239] and for patients with PIK3CA/AKT1/PTEN-altered tumours, it was 20.4 months in both arms (HR 1.05, 95% CI 0.77-1.43, P = 0.7602). At PFS DCO (25 May 2022), the median PFS in the overall population numerically favoured capivasertib-paclitaxel (5.6 versus 5.1 months placebo-paclitaxel; HR 0.72, 95% CI 0.61-0.84); this was also the case in patients with PIK3CA/AKT1/PTEN-altered tumours (7.5 versus 5.6 months placebo-paclitaxel; HR 0.70, 95% CI 0.52-0.95). The most frequent adverse event (AE) of grade ≥3 was diarrhoea [12.7% versus 0.7% placebo-paclitaxel (overall population)]. Capivasertib was discontinued due to AEs in 8.5% of patients (4.9% placebo-paclitaxel; overall population); AEs led to death in 4.2% of all patients. CONCLUSIONS: Capivasertib-paclitaxel did not meet the prespecified boundary for improving OS in either population; PFS numerically favoured the combination, especially in PIK3CA/AKT1/PTEN-altered tumours. The safety of capivasertib-paclitaxel was generally manageable and consistent with prior studies.