Novartis’ PI3K inhibitor BYL719 has met the primary endpoint in a phase 3 breast cancer trial. The hit on the progression-free survival endpoint sets Novartis up to start talking to regulators about getting the drug to market.

BYL719 is an alpha-specific PI3K inhibitor in development as a treatment for hormone-receptor positive, human epidermal growth factor receptor-2 negative, PIK3CA-mutant breast cancer. Links between PI3K and tumor development have attracted multiple companies to the target, but results have underwhelmed. Some companies, Novartis included, have seen drugs disappoint in the clinic, while the first product to reach the market—Gilead’s Zydelig—was undermined by safety problems.

Drugmakers have continued to pursue PI3K inhibitors against this backdrop, resulting in signs the field may be in recovery. Roche linked its alpha-specific PI3K inhibitor taselisib to a small PFS gain in a phase 3 breast cancer trial in June. And now Novartis has shared a superficially upbeat look at data from its rival candidate, BYL719.

Novartis’ trial enrolled 572 patients and randomized them to receive oral BYL719 or placebo on top of injections with AstraZeneca’s Faslodex. The trial linked BYL719 to improved PFS, resulting in it hitting its primary endpoint. Novartis added that the adverse events seen in the trial were "generally consistent" with earlier studies but is otherwise holding data back for an upcoming medical congress.

The release of the full data set will go some way toward showing how important a drug BYL719 could be for breast cancer patients. Until then, it is impossible to tell whether BYL719 achieved a marginal PFS improvement that will mean little in the real world or if it delivered big benefits. 

Novartis is now preparing to talk to regulators around the world about the path forward for a drug that is tipped by some analysts to rack up blockbuster sales. 

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