Acquired in the Ajax Therapeutics deal, the drug targets the dormant form of the same growth signaling enzyme that Incyte's Jakafi hits while it's in its active state. In a small phase 1 of pretreated patients, 16 of 23 hit the standard spleen shrinkage yardstick.
Lilly paid up to $2.3 billion for a hypothesis from a Sloan Kettering lab: that a pill aimed at the resting shape of a single growth-signaling enzyme could help patients with a rare bone-marrow cancer when the only approved drug, which targets the enzyme's active shape, stops working. This summer, at the European Hematology Association's EHA 2026 meeting, the hypothesis got its first human test, and the early numbers went in Lilly's direction.
Ajax Therapeutics, a New York biotech spun out of Ross Levine's lab at Memorial Sloan Kettering Cancer Center, was built around a structural-biology bet that Levine had argued for years. The target is JAK2, a kinase enzyme that drives the runaway blood-cell production behind myeloproliferative neoplasms, a group of blood cancers that includes myelofibrosis. Incyte's Jakafi, approved in 2011 and still the standard of care, binds JAK2 in its active shape. Levine's lab argued that JAK2 has a second, resting shape that current drugs miss, and that catching the enzyme in that state could matter when the active site stops responding. That idea is the engine of Lilly's bet. Lilly was an early investor in Ajax, continued to put money in through preclinical development, then closed the acquisition in 2024 with a price tag reported as up to $2.3 billion, most of it tied to milestones Ajax can earn as the drug progresses.
The first public readout of AJ1-11095, Ajax's lead molecule, came at EHA 2026 in early June, and it was framed by Lilly's head of business development and oncology, Jake Van Naarden, with the kind of language a buyer uses when it wants the market to take the bet seriously. "It works right out of the gate," Van Naarden told Fierce Biotech's Angus Liu, and the headline number that followed was that 16 of 23 patients in the dose-escalation phase 1 hit SVR35, the standard myelofibrosis yardstick of a 35 percent or greater reduction in spleen volume.
The framing is Lilly's. The trial is not built to be a verdict, and the read of the data should not be either. The 23 patients were all previously treated with a Type I JAK inhibitor, which is to say they had already failed or stopped responding to the class of drug that includes Jakafi. The design was a single-arm, dose-escalation phase 1, not a randomized comparison. The data cutoff was May 28, 2026, which means the readout has no durability beyond a few months and no quality-of-life measures. A 70 percent hit rate on a spleen endpoint in a small, single-arm trial is an early signal, not a verdict, and the next readouts on durability, randomized comparison, and patient-reported outcomes are the ones that will decide both the drug and the deal.
The competitive frame is what makes the science worth following. Myelofibrosis is not a one-drug market, but it is close to a one-mechanism market. Jakafi has held the standard-of-care slot for 15 years. Bristol Myers Squibb's fedratinib and GSK's momelotinib have also reached the field, all three of them Type I JAK2 inhibitors. A second-mechanism entrant that works after the Type I drugs fail would not just give Lilly a new product. It would also be the first structural answer to a question that has hung over the field since Jakafi was approved: what do you do when the active site stops responding? Lilly is betting that its resting-shape pill is the answer.
The "what to watch" list is shorter and cleaner than it usually is at this stage. First, durability. Spleen shrinkage at the May 28 cutoff is not the same as sustained response, and the field's hard cases are the patients whose disease finds a way around the drug after a year or two. Second, a randomized comparison. A single-arm phase 1 in pretreated patients can produce a flattering number without telling you what the drug would look like head to head against a Type I inhibitor, which is the question Lilly will eventually have to answer for regulators and payers. Third, the myelofibrosis quality-of-life measures, which were not in the EHA readout and are the endpoint that actually matters to patients. Fourth, the next milestone. The $2.3 billion price tag is contingent on Ajax hitting development and regulatory milestones, and the next EHA or American Society of Hematology (ASH) readout is when the market will get a cleaner read on whether the resting-shape hypothesis deserves the full price.
Levine, who remains Ajax's scientific cofounder and the chief scientific officer at Memorial Sloan Kettering, is the on-record scientific authority behind the bet. Van Naarden is the on-record Lilly executive carrying the deal. Both of them have skin in the framing, and the framing should be read as such. The phase 1 readout is real, the 16 of 23 number is real, and the structural-biology thesis is testable. None of that is the same as saying Lilly has earned the right to call the bet.
The next 18 months will. Durability data, a randomized comparison, the first quality-of-life readout, and the next milestone payment are all on the same calendar, and the resting shape of JAK2 will either become a standard answer or a footnote.