Why Keytruda's Price Refuses to Fall

An in-depth investigation by the International Consortium of Investigative Journalists (ICIJ) has laid bare the elaborate patent strategy behind the persistently high price of Merck's blockbuster cancer drug Keytruda (pembrolizumab). Through its Cancer Calculus project, ICIJ detailed how Merck has filed hundreds of patents to systematically block competitors and protect its revenue stream.

The Architecture of Exclusivity

Keytruda is among the best-selling prescription drugs in the world, approved for more than 30 cancer indications. Its core patents are set to expire in 2028—a moment that would normally open the door to biosimilar competition and significant price reductions.

However, ICIJ's analysis found that Merck has deployed a strategy known as "evergreening"—the practice of filing successive secondary patents to artificially extend a drug's market exclusivity period—potentially maintaining dominance through at least 2042.

Working with data provided by the nonprofit Initiative for Medicines, Access & Knowledge (I-MAK), ICIJ analyzed 180 U.S. patent applications related to Keytruda, which were linked to 1,032 additional filings worldwide. From this universe, 50 active U.S. patents were identified—held by Merck alone or jointly with partners—whose expiration dates extend roughly 14 years beyond the core patent cliff.

These patents fall into two categories. Primary patents protect the active ingredient itself: the pembrolizumab antibody and the mechanism by which it triggers an immune response. They last approximately 20 years from filing and bar biosimilar entry during that window. Secondary patents cover derivative aspects such as dosing regimens, treatment schedules, and manufacturing processes—the tools of evergreening.

A Decades-Long Industry Playbook [Historical Context]

Evergreening is not Merck's invention. It is a practice embedded across the pharmaceutical industry over decades. As patent cliffs loomed in the 2000s, companies developed increasingly sophisticated strategies to extend exclusivity. A landmark 2013 Indian Supreme Court ruling rejecting Novartis's bid to extend imatinib (Gleevec) patents became a touchstone for generic drug access policy in developing nations.

The rise of immunotherapy after 2015 intensified the complexity. Checkpoint inhibitors like Keytruda, which can be applied to dozens of cancer types, create vast surface areas for patent filing. Advocacy groups such as I-MAK have long argued that this architecture deepens health inequality: higher patent walls mean delayed generic access and greater patient burden.

What Comes Next [Expert Analysis]

The ICIJ investigation raises a fundamental question: does patent law, as currently applied to pharmaceuticals, serve patients or shareholders?

Industry analysts suggest that even after Keytruda's core patents expire in 2028, the 50 active secondary patents are likely to create substantial legal barriers to biosimilar entry without costly litigation. Legislative momentum is building in the U.S. Congress to curb evergreening practices, while the European Union is actively debating reforms to pharmaceutical intellectual property rules.

With a single course of Keytruda treatment costing thousands of dollars, delayed biosimilar access translates directly into unequal cancer survival rates across income levels globally. Merck maintains that patent-protected returns are essential to funding the research that produces breakthrough treatments. ICIJ's investigation, however, forces a harder look at who ultimately bears the cost of that innovation.