The emerging oncology biosimilars market and how employers can prepare.

By Sofia Shrestha

Senior Director of Clinical Strategy at Leap

A member who starts Keytruda today will likely organize the next two years of their life around it. In Leap's commercial claims data, a typical Keytruda patient receives about 12 infusions a year, and treatment can continue for up to two years. That means:

• Regular appointments.
• Prior authorizations to manage.
• Care to coordinate.

For plan sponsors, those appointments add up to the largest single line in commercial infusion spend: Keytruda accounts for 10.3% of commercial infusion spend in Leap's analysis of 20 million claims.

Merck has said U.S. biosimilar competition for Keytruda could begin in December 2028, with additional patents expiring in 2029 and litigation expected. For most self-insured employers, that's roughly two plan years away. 

What are biosimilars?

A biosimilar is a biologic the FDA has found to be highly similar to an already-approved biologic (or reference product), with no clinically meaningful differences in safety or effectiveness. Biologics are made in living cells and are too complex to copy exactly, so biosimilars follow a different approval pathway than traditional generics. The savings come from competition: Once a biosimilar enters a category, the reference product no longer has the market to itself.

Competition on its own won't lower what a plan pays, though. The goal for plan sponsors is to help each member get the lowest net-cost, clinically appropriate option, and that takes groundwork that starts well before any launch date.

How do biosimilars compare to other drug generics?

Generics and biosimilars play the same role in the market. Each is a lower-cost version of a brand-name drug that becomes available once the original loses protection from competition. Both reach the market through abbreviated FDA approval pathways that let manufacturers avoid repeating some of the costly clinical trials the original drug required. 

According to the FDA, biosimilars can cost less because their manufacturers rely on the agency's earlier finding that the original biologic is safe and effective, and the lower price doesn't reflect lower safety or effectiveness. 

The difference lies in the molecule itself. 

• A conventional drug like aspirin or a statin is a small molecule made through chemical synthesis, a process that produces the same active ingredient in every batch. A generic is an exact copy of that ingredient. 
• Biologics like Keytruda and Remicade are large, complex molecules grown in living cells, so no second manufacturer can reproduce one exactly. A biosimilar is that manufacturer's version of the reference product. It can never be identical, but it's built to act on the same target with the same safety and effectiveness.

The two also differ at the point of substitution. Pharmacists routinely swap a generic in for a brand-name drug. A biosimilar can be substituted that way only if the FDA has designated it interchangeable, and state pharmacy laws still apply. Designating a drug as an interchangeable doesn't make it safer or more effective than other biosimilars. 

The biggest difference for plan sponsors is what happens after launch. Generic entry usually reshapes a market quickly, but biosimilars have moved more slowly. The first infliximab biosimilar was approved in 2016, and by the end of 2021, biosimilars held only 26% of the commercial market for Remicade and its competitors. 

Payer coverage policies, rebate arrangements, and drug list decisions shape which product members actually receive. As a result, competition on its own won't lower what a plan pays. The goal for plan sponsors is to help each member get the lowest net-cost, clinically appropriate option, and that takes groundwork that starts well before any launch date.

Who’s building a Keytruda biosimilar?

At least three developers have publicly disclosed Keytruda biosimilar programs. 

• Celltrion lists its candidate, CT-P51, in Phase 3 trials. 
• Sandoz reported that its pembrolizumab program entered late-stage trials in 2024.
• Alvotech lists AVT32 in its pipeline. 

These are development milestones rather than confirmed U.S. launches, and any of them could shift with trial results, FDA review, or patent litigation.

The size of the category explains the interest. Keytruda and Keytruda Qlex generated $31.7 billion in worldwide sales in 2025. That figure is global manufacturer revenue rather than employer spending, but it shows why developers want a share of the category.

What other oncology biosimilars are in development?

Amneal and Sandoz have disclosed programs referencing Opdivo, which Bristol Myers Squibb expects to retain U.S. market exclusivity through at least 2028. Darzalex has two programs in development: Celltrion's CT-P44 and a program from Henlius and Dr. Reddy's. In August 2026 Alvotech signed an agreement to commercialize AVT34, a proposed Imfinzi biosimilar, in the U.S. 

Several of these programs are at earlier stages than Keytruda's.

4 ways you can prepare now

1. Know your oncology baseline, by product and route

Keytruda no longer comes in a single form. The FDA approved Keytruda Qlex, a subcutaneous version, in September 2025. Its worldwide sales grew from $128 million in the first quarter of 2026 to $463 million in the second. Subcutaneous versions can be more convenient for patients, and they also give a manufacturer a way to keep patients on its product as biosimilars approach.

Sales don't directly measure how many patients switched, but the trend matters. The more utilization moves to Qlex, the smaller the share of Keytruda spend a future IV biosimilar can address. 

2. Watch milestones, not just the calendar

December 2028 is a reasonable planning window, but it isn't a guaranteed launch date. Patent expiration starts the clock on competition; it doesn't promise that competition arrives. An IQVIA analysis identified 118 biologics expected to lose patent protection between 2025 and 2034. As of June 2024, only 12 of them had biosimilars in development. That snapshot covers every therapeutic area rather than oncology alone, but the lesson carries over: a patent cliff and a price drop are separate events.

For Keytruda, the milestones worth tracking include:

• Phase 3 results from the programs above
• FDA filings and approvals
• The 2029 patent expirations
• The outcome of any litigation

Celltrion's daratumumab candidate, CT-P44, references Darzalex. It is also in Phase 3 and belongs on the same watch list.

3. Confirm your partners can coordinate the switch

When a biosimilar launches, someone has to determine which product best fits each member. Someone also has to coordinate any change with the member, the prescriber, the specialty pharmacy, and the plan.

At Leap, that work runs through our preferred drug list strategy, which focuses on the lowest net-cost, clinically appropriate biologic. Our assessment weighs: 

• Payer policies
• Sourceability
• Acquisition price
• Plan-paid cost
• Coordination with the prescriber and member

A dedicated Leap Care Guide coordinates care across the member's journey across the provider, the infusion nurse, the specialty pharmacy, and the plan. That way, any transition happens on a coordinated timeline instead of landing on the member as a surprise.

Depending on pricing and coverage arrangements, the reference product sometimes remains the lowest net-cost option, and our preferred drug list reflects that when it happens.

4. Measure what the switch actually changes

Biosimilar adoption is easy to count and easy to mistake for success. A useful scorecard tracks three outcomes alongside adoption:

• Realized plan savings
• Member cost sharing
• Treatment continuity

Together, these show whether a transition lowered what the plan paid while keeping members on track with their care.

Your takeaway

The plan sponsors who benefit most from a Keytruda biosimilar or others in oncology will be the ones who know their baseline by product and route, practice on the oncology biosimilars available today, and have a partner ready to help each member reach the lowest net-cost, clinically appropriate option.

You also don't have to wait until 2028 to act on Keytruda spend. Leap bills specialty drugs at true acquisition cost, with no buy-and-bill markup, so annual savings on Keytruda through Leap can range from $60,000 to $255,000 per patient today. A claims-based savings analysis built from your own data shows what that could look like for your plan. It also gives you the product-and-route baseline that step one calls for.

Request an impact analysis from Leap today using your own data to help you understand how you can better contain rising specialty drug costs.

About the author

Sofia Shrestha is the Senior Director of Clinical Strategy at Leap. With extensive experience in managing complex pharmacotherapies for specialty and rare diseases, she brings a patient-centered approach to specialty care. Her diverse experience spans specialty pharmacy, home infusion, and ambulatory care, which she draws on to lead Leap's innovative pharmacy programs.