Merck's Diversification Imperative Amidst Keytruda Patent Expiry

Merck & Co. (MRK)'s immune checkpoint inhibitor, Keytruda (pembrolizumab), achieved unprecedented commercial success, generating approximately $31.7 billion in revenue in 2025. However, it faces a significant patent cliff, beginning with the expiration of its U.S. patent in December 2028. With the anticipated surge of biosimilars, filling the void left by Keytruda, which accounts for nearly half of the company's revenue, will be challenging. Therefore, Merck is strategically expanding its pipeline into diverse disease areas, alongside the development of Keytruda Qlex, a subcutaneous formulation. This approach aims to reduce reliance on a single blockbuster and diversify risks to establish a sustainable long-term growth foundation.

New Blockbuster Potential in Cardiovascular and Respiratory Fields

To mitigate the development risks associated with novel drug candidates, Merck is pursuing a strategy of acquiring late-stage assets, focusing on the cardiovascular and respiratory fields as its second growth engine. The acquisition of Acceleron Pharma in 2021 for $11.5 billion brought Winrevair (sotatercept), a pulmonary arterial hypertension treatment, which demonstrated strong commercial potential with $1.4 billion in revenue in 2025. Furthermore, the acquisition of Verona Pharma in October 2025 added Ohtuvayre (ensifentrine), a novel treatment for chronic obstructive pulmonary disease (COPD), and the recent FDA approval of Lipfendra (enlicitide), the first oral PCSK9 inhibitor, further strengthens Merck's cardiology portfolio.

Expanding Immunology Territory with Tulisokibart and Competitive Landscape

In the autoimmune disease area, Tulisokibart, an anti-TL1A antibody acquired through the $10.8 billion acquisition of Prometheus Biosciences in 2023, has emerged as a key asset. Tulisokibart demonstrated efficacy in a Phase 3 trial (ATLAS-UC) for ulcerative colitis in June 2026, solidifying its position as a first-in-class drug and establishing a clinical advantage over duvakitug, a competing product from Sanofi and Teva. Merck intends to expand the use of this drug to other inflammatory diseases, such as Crohn's disease, replicating the successful expansion strategy employed by Keytruda in the oncology field.

Diversifying Pipeline with Infectious Disease and Oncology Innovations

In the infectious disease area, MK-1406, an influenza vaccine acquired through the $9.2 billion acquisition of Cidara Therapeutics in January 2026, and islatravir, a once-weekly HIV treatment developed in collaboration with Gilead Sciences (GILD), have shown positive data in Phase 3 trials. Additionally, the acquisition of Terns Pharmaceuticals (TERN) in March 2026 brought TERN-701, a treatment for chronic myeloid leukemia. Furthermore, Merck is accelerating the development of new platforms, including a personalized cancer vaccine in collaboration with Moderna (MRNA). Merck is now transitioning from a high-margin structure reliant on a single oncology drug to a diversified, comprehensive healthcare company that must simultaneously manage numerous complex late-stage clinical trials and regulatory processes.