How Merck’s Patent Strategy Delays Keytruda Competition Until 2042

Merck’s Patent Strategy Could Extend Keytruda Monopoly Until 2042, Investigation Finds

An investigation by the International Consortium of Investigative Journalists (ICIJ) has revealed how pharmaceutical giant Merck & Co. Is using an aggressive patent strategy to delay competition for its blockbuster cancer drug Keytruda, potentially extending its market exclusivity for nearly 15 years beyond the expiration of its core patents in 2028.

The Cancer Calculus investigation, published April 13, 2026, found that Merck has built a “fortress” of 50 active U.S. Patents around Keytruda, a strategy known as “evergreening” that could keep cheaper biosimilar versions off the market until at least 2042. The drug, which generated over $25 billion in global sales in 2025, is one of the world’s top-selling cancer treatments.

How Evergreening Works

Merck’s original patents for Keytruda, which cover the drug’s active ingredient and primary mechanism of action, are set to expire in 2028. Under normal circumstances, this would allow competitors to introduce biosimilars—near-identical versions of the drug—at significantly lower prices. However, the ICIJ analysis shows that Merck has filed hundreds of additional patents to extend its control over the drug.

These secondary patents cover aspects beyond the core molecule, including new dosing regimens, manufacturing processes, and combinations with other drugs. While individually narrower than the original patents, collectively they create a “patent thicket” that deters competitors by increasing the risk of costly legal battles over infringement.

“Active patents are central to evergreening because they carry defined expiration dates that can extend market exclusivity,” the ICIJ report states. The investigation, which analyzed 180 U.S. Patent applications provided by the nonprofit Initiative for Medicines, Access & Knowledge (I-MAK), found that these patents could protect Keytruda’s dominance through at least 2042.

Global Patent Web

The ICIJ’s review identified 1,032 patent filings related to Keytruda across 53 countries, regions, and territories. In the U.S. Alone, Merck holds 50 active patents, either filed independently or in partnership with other entities. These patents vary in scope, with some covering specific treatment schedules and others protecting manufacturing techniques.

Primary patents protect the drug’s active ingredient, while secondary patents extend protection to peripheral innovations. “Secondary patents are follow-on patents that protect aspects of an existing drug beyond the primary patent protection of the original active ingredient,” the ICIJ explains. “They can cover new dosing amounts, different treatment schedules, manufacturing processes, or combinations with other drugs.”

Impact on Patients and Healthcare Systems

Keytruda’s high cost—often exceeding $150,000 per patient per year in the U.S.—has made it a focal point in debates over drug pricing. The ICIJ investigation highlights how Merck’s patent strategy contributes to these costs by delaying competition. Without biosimilars, patients and healthcare systems may continue paying premium prices for the drug long after its original patents expire.

A 2021 study by I-MAK found that Merck filed 129 patent applications for Keytruda, more than half of which were submitted after the drug’s initial FDA approval in 2014. This pattern of post-approval filings is a common tactic in the pharmaceutical industry to prolong monopolies, the report notes.

The investigation also points to Merck’s lobbying efforts to avoid price negotiations with Medicare, further insulating Keytruda from cost pressures. While studies have suggested that lower, weight-based doses could be equally effective and reduce expenses, the company has not adjusted its dosing strategy.

Legal and Regulatory Challenges Ahead

Merck has signaled confidence in its ability to defend Keytruda’s patent estate beyond 2028. During a fourth-quarter earnings call in early 2026, company executives noted that while the core compound patent expires in December 2028, two additional patents—a method-of-making patent expiring in May 2029 and a method-of-use patent expiring in November 2029—could further delay biosimilar entry.

However, the ICIJ’s findings suggest that the broader patent thicket could pose a more significant barrier. Competitors may hesitate to challenge Merck in court, given the complexity and cost of navigating the overlapping patents. This dynamic has played out with other blockbuster drugs, where secondary patents have successfully delayed generic or biosimilar competition for years.

Broader Implications for the Pharmaceutical Industry

The Keytruda case underscores a growing concern among policymakers and patient advocates about the use of evergreening to extend drug monopolies. Critics argue that the practice prioritizes corporate profits over patient access, particularly for life-saving medications. The ICIJ investigation notes that similar strategies are employed by other pharmaceutical companies to protect high-revenue drugs.

“Merck protects the drug from generic competition behind a growing wall of patents,” the report states. “The company lobbies to avoid negotiating the price of the drug with Medicare. And though studies have said lower doses based on weight are effective and would save money, the company has not moved to change dosing.”

As the 2028 expiration date for Keytruda’s core patents approaches, the debate over patent reform and drug pricing is likely to intensify. The ICIJ’s findings add fuel to calls for stricter regulations on secondary patents and greater transparency in the pharmaceutical industry’s patent filings.

Reporting contributed by Denise Ajiri, Miguel Fiandor-Gutiérrez, Delphine Reuter, Joanna Robin, Hamish Boland-Rudder, and Annys Shin. Data sourced from I-MAK, Espacenet, and Google Patents.