Merck's Keytruda Sustains Revenue Growth as Diversification and Legal Risks Loom

What happened

Merck's Keytruda, a PD-1 inhibitor, accounted for 55% of pharmaceutical sales and drove the 2025 revenue surge, reinforcing its dominance in oncology. However, DeepValue's report notes Keytruda generated $31.7B in FY2025 sales, up 7% YoY, highlighting heavy reliance ahead of the 2028 loss-of-exclusivity cliff. To counter this, Merck is expanding labels, pursuing a subcutaneous formulation, and reorganizing into separate oncology and non-oncology units to boost accountability and launch execution. Critical risks include a preliminary injunction against Keytruda SC in Germany and ongoing U.S. litigation, which could fragment lifecycle defenses and delay commercialization. Meanwhile, diversification through newer products like WINREVAIR and acquisitions such as Cidara's CD388 program faces execution hurdles, including a ~$9.0B FY2026 charge, pressuring the post-Keytruda transition.

Implication

Merck's stock is highly sensitive to Keytruda's durability, with any growth deceleration or legal setbacks potentially triggering significant downside. The organizational split aims to improve launch speed, but investors need concrete evidence in upcoming SEC filings to validate operational changes. Legal risks around the subcutaneous Keytruda formulation, especially the German injunction, require close monitoring as they could limit market access and erode competitive advantages. Diversification efforts, including Cidara's CD388 and newer products, must scale quickly to offset Gardasil's decline and prepare for the 2028 LOE, yet integration and trial outcomes add uncertainty. With a base case implied value of $135 and current price near $124, the margin for error is narrow, demanding disciplined tracking of catalysts like CD388 Phase 3 updates and segment reporting.

Thesis delta

The Zacks article confirms Keytruda's central role in Merck's revenue, aligning with the DeepValue report's emphasis on product concentration risk. However, it lacks critical depth on looming challenges like the 2028 LOE and legal issues, so it does not shift the investment thesis but reinforces the need for vigilance on diversification and execution milestones.