Lilly scores early positive data for new JAK drug

An article from Lilly scores early positive data for new JAK drug Acquired through its purchase of Ajax, the drug showed encouraging effects in patients with hard-to-treat myelofibrosis. To analysts, such results could lead to competition for Incyte’s Jakafi. Published June 15, 2026 Jacob Bell Lead Reporter Share Copy link Email LinkedIn X/Twitter Facebook Print License Add us on Google An experimental drug that Eli Lilly recently picked up through a potentially multibillion-dollar acquisition appears to have passed its first major test, scoring positive results in a small study of patients with hard-to-treat blood cancer. Originally developed by Ajax Therapeutics, the drug inhibits an enzyme that spurs blood cell production. Several medicines that block this “JAK2” enzyme, including Incyte’s Jakafi, are already on the market, where they’re mostly used in rare, chronic blood cancers like myelofibrosis. While these medicines can be quite effective at treating symptoms, many patients either don’t respond or stop taking them because their disease progresses or they can’t tolerate the side effects, which range from nausea and fatigue to anemia and increased stroke risk. Lilly’s pill is designed to work in a slightly different way than its approved counterparts, binding to JAK2 in the “inactive” state. Researchers hypothesize this change should make for a superior therapy that also overcomes drug resistance challenges. That idea now has more support thanks to data presented over the weekend at a major medical meeting in Europe. There, researchers shared that, among 20 patients who had been receiving Lilly’s drug for 12 weeks and underwent body imaging, 13 achieved a 35% reduction in spleen volume. That kind of measurement is often used to assess whether JAK therapy is working, since a hallmark characteristic of myelofibrosis is a swollen spleen. Another four participants experienced a spleen deflation between 25% and 34%. The study evaluated five doses of Lilly’s drug that grew in increments of 25 milligrams, up to the highest dose of 125. Researchers said increasing the dose led to two more patients hitting the milestone of 35% spleen volume reduction. Additionally, after their first treatment cycle, 17 participants achieved what’s considered the gold standard of a myelofibrosis drug trial: a 50% or more reduction in total symptoms. This measure provides a snapshot of a patient’s quality of life and whether they’ve noticed changes in any prevalent symptoms like tiredness, itching, pain or night sweats. The study enrolled people with myelofibrosis who were previously treated with a medicine that docks onto JAK enzymes in their “active” form. Though early, the effects Lilly’s drug showed in this group “are encouraging and suggest meaningful improvements over other investigational agents,” according to Leerink Partners analyst Andrew Berens. If Lilly continues to generate positive results in larger experiments, that could lead to greater competition in the JAK market. In myelofibrosis, Lilly’s drug “looks to have the makings of a better Jakafi,” wrote Jefferies analyst Faisal Kurshid in a note to clients Sunday. Shares of Incyte were down more than 5%, to just under $103 apiece, in late morning trading Monday. Last year, Incyte recorded almost $3.1 billion from Jakafi sales, which accounted for 71% of the company’s net product revenue. Recommended Reading Lilly to buy startup Ajax in bid for a better JAK drug By Ben Fidler • April 27, 2026 Add us on Google Share Copy link Email LinkedIn X/Twitter Facebook Print License Filed Under: Pharma, Clinical Trials