Retail Traders Bet on SLS, MLTX as Merck Eyes Biotech Deals Ahead of Keytruda's $31.7B Patent Cliff in 2028

According to Stocktwits sentiment data as of July 12, retail traders are actively betting on Sellas Life Sciences (SLS) and MoonLake Immunotherapeutics (MLTX) as potential acquisition targets for Merck & Co. (MRK) as the drugmaker prepares for the approaching loss of exclusivity for its flagship cancer drug Keytruda. Keytruda generated $31.7 billion in 2025, accounting for 55% of Merck's pharmaceutical revenue, with the U.S. patent cliff beginning in 2028.

SLS bulls are focused on the company's galinpepimut-S (GPS) immunotherapy, which is nearing its Phase 3 final analysis in acute myeloid leukemia treatment with 78 of 80 required patient-death events recorded. MLTX has the advantage of prior Merck interest, with Financial Times reporting that Merck submitted a nonbinding offer valuing MoonLake at over $3 billion last year. David Giroux, chief investment officer at T. Rowe Price, told Barron's that large pharma faces a $400 billion to $500 billion patent-expiration hole over the next decade, expecting "tremendous" small and mid-cap biotech acquisitions at 50% to 100% premiums, naming MoonLake as a potential target.