Alongside chemoradiation therapy (CRT), Merck’s PD-1 inhibitor failed to meet its primary endpoint in a late-stage trial for unresected locally advanced head and neck squamous cell carcinoma (HNSCC). While the drug did chart improvements versus placebo in event-free survival, or the time a patient remains free of complications, the results weren’t statistically significant, Merck said in a release.

The study, which enrolled around 780 newly diagnosed HNSCC patients, pitted Keytruda and concurrent chemoradiation against placebo, the chemotherapy cisplatin and CRT. After completing the Keytruda regimen, patients in the treatment arm received the drug alone as a maintenance therapy for roughly one year, Merck said. Patients in the control arm received placebo after completing their placebo, cisplatin and CRT regimen.

“There have been limited advances for patients with locally advanced HNSCC, and unfortunately, these results suggest that this disease remains very challenging to treat,” Eliav Barr, M.D., senior vice president, head of global clinical development and chief medical officer at Merck Research Laboratories, said in a statement. He said Merck remains committed to studying Keytruda in earlier stages of HNSCC.

The New Jersey-based drugmaker plans to share the results of its phase 3 KEYNOTE-412 trial at an upcoming medical meeting.

Keytruda clinched its first head and neck cancer nod back in 2016, beating archrival Opdivo from Bristol Myers Squibb to an approval to treat advanced disease in patients who’ve failed on platinum-based chemotherapy.

In 2019, meanwhile, the drug scored a double green light in previously untreated head and neck cancer patients, winning FDA clearance as both a monotherapy for patients whose tumors bear the PD-L1 biomarker and in combination with chemo for patients regardless of their PD-L1 status.

As the first PD-1/PD-L1 drug to break into the first-line market, Keytruda is currently approved for more patients with head and neck cancer than Bristol Myers Squibb’s Opdivo is. Bristol’s drug, for its part, is only cleared for patients who’ve already failed on chemotherapy.

Head and neck cancer covers a range of tumors that develop in or around the throat, larynx, nose, sinuses and mouth, Merck explained. Worldwide, more than 930,000 new cases were diagnosed and more than 465,000 people died from the disease in 2020, according to Merck’s estimates.

Keytruda continues to line Merck’s pockets as the company’s top-selling drug. Over the first three months of the year, Keytruda sales climbed 23% to $4.8 billion, Merck reported in April. Overall, Keytruda sales jumped 20% to $17.2 billion for all of 2021.

Meanwhile, as Merck inches closes to the megablockbuster’s patent expiration later this decade, the company is looking for ways to diversify its marketed and pipeline portfolios. As one tactic, the company is reportedly eyeing cancer specialist Seagen in a potential $40 billion pickup.