Phosphoinositide 3-kinase inhibitors in advanced breast cancer: A systematic review and meta-analysis

Phosphoinositide 3-kinase (PI3K) inhibitors may overcome drug resistance and improve advanced breast cancer (ABC) outcomes. We conducted a systematic review and meta-analysis to assess the efficacy and safety of adding a PI3K inhibitor to the standard of care (SOC) treatment in ABC. The electronic databases Ovid, PubMed, Cochrane Central Register of Controlled Trials and Embase, were searched for relevant randomised trials. Pooled hazard ratios (HRs) for progression-free survival (PFS) and pooled risk ratios (RRs) for objective response rates (ORRs), disease control rates (DCRs) and toxicity were meta-analysed using the Mantel-Haenszel method and generic inverse variance. Five studies were included. In unselected patients, the addition of a PI3K inhibitor decreased the risk of progression by 21% (2329 participants, HR = 0.79; 95% confidence interval [CI], 0.71-0.88). A marginal improvement in ORR (2329 participants, RR = 1.26; 95% CI, 1.01-1.57) and no improvement in DCR (2146 participants, RR = 1.05; 95% CI, 0.94-1.18) were achieved with a significant increase in toxicity of any grade (2386 participants, RR = 1.05; 95% CI, 1.03-1.06) and of grade III and higher (2386 participants, RR = 1.91; 95% CI, 1.76-2.08). A PFS benefit was seen in patients with and without PI3K pathway activation assessed on tumour and only in patients with an activated PI3K pathway when it was assessed from the plasma using circulating tumour DNA (ct-DNA) analysis. The addition of a PI3K inhibitor decreases the risk of progression in unselected ABC patients and particularly in patients with an activated PI3K pathway detected on ct-DNA analysis. However, their significant dose-limiting toxicity is a limiting factor. Selective PI3K inhibitors are being tested to assess whether these better-tolerated agents have a role in ABC treatment.