GSK limits Zejula's ovarian cancer use after dodging FDA expert hearing. Will others follow?

The safety brouhaha around PARP inhibitors’ use in ovarian cancer is taking yet another turn. 

At the request of the FDA, GSK is moving to restrict Zejula’s second-line maintenance ovarian cancer indication in the U.S. to only cover patients with germline BRCA mutations, the company said Friday. Before the move, GSK already pulled Zejula’s approval in late-line ovarian cancer.

The decision comes after GSK avoided a potentially contentious FDA advisory committee meeting. The FDA cancelled the meeting a few days ago, raising expectations among industry watchers that the agency had reached an agreement with GSK.

GSK’s move could bring ripple effects, potentially affecting other PARP inhibitors in AstraZeneca and Merck’s Lynparza and Clovis Oncology’s Rubraca.

Maintenance treatment of recurrent ovarian cancer in responders to chemotherapy was Zejula’s first FDA nod, gained in 2017 based on tumor progression benefit observed in the phase 3 Nova trial. In a big win at that time, Zejula was the first PARP inhibitor for patients regardless of their BRCA mutation status.

But a longer-term follow-up of the Nova study found that Zejula increased the risk of death by 10% in patients whose tumors didn’t bear germline BRCA mutations, according to data presented at the Society of Gynecologic Oncology 2021 annual meeting. Those who took the GSK drug lived a median 31.1 months, versus 36.5 months for placebo. After adjusting for follow-on PARP inhibitor use, investigators found no difference in patient survival between the trial arms in the patient subgroup.

Meanwhile, in the BRCA-mutant group, Zejula reduced the risk of death by 7%, and the risk reduction widened to 34% after adjusting for follow-on PARP inhibitor use.

“Based on the totality of evidence available to GSK, there is no change to the benefit/risk profile for [Zejula] in the non-gBRCAm patient population,” GSK said in a statement Friday, adding that it’s only complying with the FDA’s request to install the new restriction.

Before the latest revelation, FDA had first cracked down on PARP inhibitors’ fourth-line ovarian cancer use based on even more concerning patient survival results from Clovis’ Rubraca in that setting. Under FDA’s pressure, Rubraca, Zejula and Lynparza have all withdrawn their late-line indications.

PARP inhibitors have shown a strong ability to stave off tumor progression, but the discrepancy with life extension data has raised the theory that side effects for this class of drugs may be a larger problem over the longer term.

Now, just as how Rubraca’s ARIEL4 trial triggered a classwide retreat from late-line treatment, Zejula’s latest restriction could also have wider effects.

Even before GSK’s Friday announcement, Clovis warned that the FDA might come after Rubraca’s second-line maintenance indication should Zejula’s use be narrowed. Rubraca’s data there also make the drug vulnerable to scrutiny.

Clovis’ Rubraca won its own second-line maintenance nod in 2018, also in an all-comers population regardless of biomarker status. The approval was supported by data from the ARIEL3 trial showing Rubraca reduced the risk of tumor progression or death.

But the final overall survival analysis presented at this year’s International Gynecologic Cancer Society congress found Rubraca conferred no patient survival benefits in the overall trial population.

In the BRCA-mutant group, Rubraca cut the risk of death by 17%. But in patients without BRCA mutations and with high level of genetic abnormality called loss of heterozygosity, Rubraca was linked to a 28% increased risk of death. And in non-BRCA-mutant patients with low loss of heterozygosity, the Clovis drug had a 15% increased risk of death.

Second-line maintenance ovarian cancer is currently Rubraca’s main source of revenue. A label restriction there would push Clovis closer to a potential bankruptcy, as the company indicated Wednesday in a quarterly filing.

In response to a Fierce Pharma request for comment, Colorado-based Clovis said it didn’t have further information beyond the securities filing.

Lynparza, currently the PARP market leader, is perhaps in better shape. A final overall survival analysis of the phase 3 SOLO2 trial found Lynparza cut the risk of death by 26% over placebo when used as maintenance treatment in patients with relapsed ovarian cancer and a BRCA mutation.

In a phase 2 trial coded Study 19 that also helped Lynparza win its second-line maintenance approval in 2017, the drug pared down the risk of death by 16% in patients without BRCA mutations in its final analysis.

AstraZeneca has yet to respond to Fierce Pharma inquiry by publication time.

The patient pool in the second-line maintenance setting is dwindling now that PARP inhibitors have moved to the frontline maintenance setting in newly diagnosed patients who’ve responded to chemo. There, GSK has an all-comers first-line indication for Zejula, and the British drugmaker on Friday said that use remains unchanged.