AstraZeneca delays PD-L1 data in rejig of phase 3 program

AstraZeneca HQ
AstraZeneca has tweaked the phase 3 program for its immuno-oncology hopefuls

AstraZeneca has pushed back the estimated completion date for the phase 3 trial of its PD-L1 drug, a first-line treatment for non-small cell lung cancer (NSCLC). Progression-free survival data are now due to drop in the middle of this year, with an overall survival readout set to follow by 2018 at the latest.

Prior to the update, AstraZeneca expected to complete the first part of the MYSTIC study this month, with publication of PFS data due to follow in the first half of the year.

AstraZeneca tweaked its timeline in response to changes it made to the study protocol last year. In February, AstraZeneca upped its targeted enrollment from 675 to 780. Three months later the Big Pharma boosted the target once again—bringing it up to 1092—as part of an update that added OS to the primary endpoint.

Prior to that May update, the primary endpoint was limited to PFS. When paired to the event-based nature of the study, those changes—which were made without moving the primary completion date from January 2017—led to the revised timeline.

The big Pharma disclosed the new timeline alongside other tweaks to MYSTIC and its broader PD-L1 clinical trial program. Notably, MYSTIC will now take a closer look at PD-L1 drug durvalumab as a monotherapy, while continuing to assess its use in combination with CTLA-4 monoclonal antibody tremelimumab.

“The MYSTIC trial will now assess PFS and OS endpoints in patients with PDL1-expressing tumours for both durvalumab monotherapy and the combination of durva + treme, as well as in ‘all comers’ for the combination of durva + treme, versus [standard-of-care] chemotherapy."

“While the focus remains on exploring the benefit of durva + treme as combination therapy, the company has updated the endpoints of the MYSTIC trial to include OS and PFS in durvalumab monotherapy,” AstraZeneca wrote in a statement to disclose the changes.

AstraZeneca attributed its decision to add endpoints for durvalumab as a monotherapy to “recent internal and external data” and “significant opportunities in the competitive landscape.” The drug is AstraZeneca’s pitch for the increasingly congested PD-1/PD-L1 niche, which is currently being contested by Bristol-Myers Squibb, Merck and Roche.

In stepping up its interest in the monotherapy, AstraZeneca has created a source of debate for those trying to read the tea leaves. As Bernstein Analyst Tim Anderson put it, “Bulls will claim it is smart for AZN to hedge its bets with both mono- and combination therapy. Bears will claim AZN may have less confidence than before in the CTLA4 combination approach, which has been at the core of its IO development program.”

CTLA-4 drug Tremelimumab could play the same role in AstraZeneca’s pipeline and combination therapies as Yervoy does in those of Bristol-Myers. But with a failure in mesothelioma against its name and a limited pool of data on its safety and efficacy from other studies, it remains something of a wildcard.

The combination of tremelimumab and durvalumab is the focus of NEPTUNE, another of the trials AstraZeneca altered this week. That phase 3 will now add local patients to allow AstraZeneca to swing for a first-line NSCLC approval in China without pushing back OS data from the global cohort. AstraZeneca further refined its Asian strategy by kicking off another phase 3, PEARL, that will test durvalumab monotherapy in NSCLC patients whose tumors express PD-L1.