The Best-Selling Drug Just Met Its Copycat

First Across the Finish Line (Sort Of)

Samsung Bioepis is now the first company to disclose global Phase 3 data for a Keytruda biosimilar. That's a meaningful head start in a race with at least ten entrants.

The competition reads like a biotech all-star roster. Sandoz is running Phase 1 and Phase 3 trials with its candidate GME751. Celltrion has Phase 3 studies underway. Formycon, partnered with Zydus Lifesciences for North America, reported positive Phase 1 results in February 2026 and is pursuing a streamlined FDA pathway that might skip a full Phase 3 entirely. Alvotech teamed up with Dr. Reddy's in June 2025, though their candidate is still preclinical.

Then there's mAbxience, Bio-Thera Solutions, and Shanghai Henlius, all pushing their own programs forward.

Being first with data doesn't guarantee being first to market. But it does mean Samsung Bioepis can file for regulatory approval sooner, potentially submitting a U.S. application (called a 351(k) biosimilar filing) as early as this year. That positions them for a possible launch right around Keytruda's key U.S. patent expiration in 2028.

The Patent Cliff That Keeps Merck Up at Night

Merck knows what's coming. The company has been running one of pharma's most aggressive lifecycle playbooks to protect its crown jewel.

Keytruda's core U.S. patents for the IV formulation start expiring around 2028. In Europe, supplementary protection certificates push that date to 2031. Some U.S. patents technically extend to 2036, but the practical window for biosimilar competition opens much sooner.

So Merck faces a one-two punch of biosimilar competition and potential Medicare price controls arriving in quick succession.

Merck's counter-strategy? A new subcutaneous version called Keytruda Qlex, launched in 2025. It's a clever move. Biosimilar developers are building copies of IV Keytruda. A subcutaneous formulation is a different product with different patents, potentially keeping patients on the branded version even after IV biosimilars arrive. Think of it like switching from DVD to streaming right before someone builds a cheaper DVD player.

Analysts project Keytruda could reach roughly $35 billion in annual sales before meaningful competition hits. That's a lot of revenue to defend.

What Cheaper Keytruda Could Mean for Patients

This is where the story gets genuinely exciting. Keytruda is extremely expensive for patients in the U.S. without broad insurance coverage. Biosimilars are expected to launch at 20 to 30% discounts, and those discounts tend to deepen as more competitors enter the market.

Scale biosimilar pricing globally, and you're talking about millions of cancer patients in middle-income countries gaining access to a therapy that was previously out of reach.

PD-1 inhibitors like Keytruda have genuinely transformed cancer treatment over the past decade. They work by helping the immune system recognize and attack tumors, a concept called checkpoint inhibition. The problem has never been whether they work; it's been whether health systems can afford them for everyone who might benefit.

Biosimilars could change that equation dramatically.

The Bigger Picture: PD-1 Goes Generic

Zoom out and something fascinating is happening. The entire PD-1/PD-L1 checkpoint inhibitor class, which includes Bristol Myers Squibb's Opdivo, Roche's Tecentriq, and AstraZeneca's Imfinzi, is slowly transitioning from premium innovation to commodity backbone.

When biosimilars commoditize the foundation of immuno-oncology, the real value shifts upstream. Next-generation combinations, bispecific antibodies, and novel immune targets become the new frontier where companies can charge premium prices. The PD-1 inhibitor itself becomes the "generic backbone" that everything else gets stacked on top of.

For Samsung Bioepis, the clinical risk on SB-27 now looks low. The remaining hurdles are regulatory timelines, patent litigation outcomes, and commercial execution. No approved Keytruda biosimilar exists in any major market yet. 2026 is the year of filing; 2028 is the year of launching.

But after this week's data, the countdown to cheaper Keytruda officially started. And for the world's best-selling drug, that clock is ticking loud.