By collapsing EED and EZH2 into a single regulatory class, the FDA turned one withdrawn cancer drug's safety signal into a precedent that will shape epigenetics drug development for years.
The FDA didn't just discontinue a sickle cell drug this month. It drew a regulatory line through the entire PRC2 inhibitor class — and in doing so, it closed off a working therapeutic option for sickle cell disease while signaling to every developer in the epigenetics space what class-level safety evidence now means in practice.
On June 1, 2026, Cambridge-based Fulcrum Therapeutics (Nasdaq: FULC) announced it was discontinuing its pociredir program in sickle cell disease (SCD) and launching a comprehensive review of strategic alternatives to maximize stockholder value. The company framed the decision as a response to end-of-Phase FDA interactions in which the agency, in meeting minutes delivered May 28, raised heightened concerns about pociredir's benefit-risk profile in SCD.
The FDA's reasoning — disclosed by Fulcrum and corroborated by trade press — rested on a class-effect read-across: secondary malignancies observed with Tazverik (tazemetostat) and the drug's subsequent global withdrawal in March 2026, applied to pociredir's benefit-risk assessment as a member of the broader PRC2 inhibitor class. Pociredir and tazemetostat both sit within the same regulatory neighborhood, which the agency treated as a single safety envelope.
That is consequential for two reasons. First, pociredir was not a failed drug. In the Phase 1b PIONEER trial, the 20 mg dose cohort produced positive 12-week results — a clinical activity signal that, in another regulatory frame, might have supported continued development in a high-need population. The discontinuation is the loss of a therapeutic option, not just the end of a program.
Second, Fulcrum's mechanistic counter-argument was rejected. Pociredir targets EED, a PRC2 complex member distinct from the EZH2 active site that tazemetostat inhibits. Fulcrum argued that the two compounds are biologically separable. The FDA, according to the meeting minutes summarized in the company's discontinuation release, did not accept that distinction. The agency treated the class-level signal as controlling.
That decision now travels. Trade coverage from GEN frames the discontinuation alongside the open-ended strategic review Fulcrum has launched; the more durable story is what the ruling tells the next developer who tries to argue biology against a class-wide safety signal. When a regulator collapses two mechanistically distinct targets into one class, the burden of disentangling them shifts to the sponsor — and the bar is now visible.
For SCD patients, the immediate consequence is a narrower pipeline in a disease with limited disease-modifying options. For the broader field, the precedent is a working example of how FDA class-effect logic accumulates: one withdrawn drug's safety record, applied across a class, can foreclose development paths that have produced genuine clinical activity.
Fulcrum, for its part, has said it is evaluating strategic alternatives in its Q1 2026 update — a process whose outcome is not yet known. The harder, longer-running story is the regulatory line the FDA just drew, and the epigenetics programs that will now have to design around it.