Merck's Tulisokibart Meets Endpoints in Hidradenitis Suppurativa Study

Merck's phase IIb tulisokibart study in moderate-to-severe hidradenitis suppurativa met its primary HiSCR50 endpoint at week 16: response rates were 72% for the 480 mg every-two-weeks dose and 64% for the 480 mg every-four-weeks dose, versus 35% for placebo. HiSCR75 responses reached 41% and 40% for the high- and medium-dose arms, respectively, versus 15% for placebo, alongside improved quality-of-life measures. Merck plans to advance the anti-TL1A antibody into phase III for HS, adding to ongoing development across six immune-mediated indications.

Analysis

The incremental valuation relevance is less HS revenue than platform de-risking: a positive dermatology signal supports the biological breadth of TL1A and modestly raises probability-of-success assumptions for the much larger IBD programs. That matters for MRK's post-Keytruda loss-of-exclusivity narrative, but phase II efficacy alone does not establish commercial differentiation versus established immunology franchises; durability, infections, discontinuations and dose-dependent safety will determine whether the asset earns premium positioning.

Competitive pressure falls most directly on AbbVie's legacy HS exposure and, at the margin, UCB's Bimzelx and Novartis's Cosentyx as treatment algorithms broaden. However, switching in HS is constrained by payer step edits and physician familiarity, so any share effect is a multi-year issue rather than a near-term earnings risk. Roche's TL1A exposure is the cleaner competitive read-through: validation of the mechanism may improve its asset's strategic value, while simultaneously raising the efficacy and safety threshold required in IBD.

The likely immediate MRK move should be restrained because the indication is not a near-term earnings driver and the stock has already rerated. Over the next 1-3 months, watch for management disclosure on phase III design, dose selection, safety and manufacturing capacity; 6-18 month upside depends primarily on IBD data and whether management can translate a multi-indication pipeline into credible replacement cash flows. The thesis is falsified by safety imbalances, weak durability beyond induction, or phase III designs that imply a slow and expensive path to an approvable label.

Key Decisions for Investors

• Maintain MRK as a modest core long, but do not chase a data-driven gap; add only on a 5-8% pullback or if subsequent disclosures confirm clean safety and a commercially viable every-four-week regimen. Risk/reward is better over 12-24 months than over the next quarter, with IBD execution—not HS—being the valuation catalyst.
• Use a small long MRK / short ABBV relative-value position over 6-12 months only if MRK provides supportive IBD updates; the trade expresses diversification of MRK's immunology pipeline against AbbVie's mature, highly penetrated inflammatory-disease franchise. Exit if MRK reports a meaningful safety signal or AbbVie demonstrates accelerating Skyrizi/Rinvoq immunology growth.
• Place an alert on Roche (RHHBY): positive cross-asset TL1A validation can support pipeline optionality, but wait for comparable efficacy, durability and safety data before initiating exposure. Mechanism validation alone is insufficient to underwrite an IBD competitive advantage.
• Avoid treating ACIU, AMRN, ARQT or QBTS as beneficiaries of this development; their inclusion is not a fundamental read-through and creates avoidable single-name noise.