Fulcrum Therapeutics Touts PIONEER HbF Gains, Early VOC Signal; FDA Path and Accelerated Approval Talk

17 Mar 2026, 01:32 by Mitch Edgeman · The Markets Daily

Fulcrum Therapeutics (NASDAQ:FULC) executives highlighted what they described as strong physician interest and encouraging clinical signals from the company’s PIONEER study in sickle cell disease during a recent discussion hosted by Leerink Partners equity research analyst Joe Schwartz.

PIONEER takeaways: HbF induction, hemolysis markers, and early VOC signal

Chief Executive Officer Alex Sapir said feedback from the physician community following the company’s release of full PIONEER data has been “overwhelmingly positive,” citing two primary factors. First, he pointed to what he called robust and rapid induction of fetal hemoglobin (HbF), which he linked to the established relationship between higher hemoglobin and fewer vaso-occlusive crises (VOCs). Sapir said patients entered the study at 7.1 and reached 19.3 by the end of the 12-week study, describing that as a delta of 12.2.

Second, Sapir emphasized the “totality of the data,” noting that key markers associated with hemolysis—including LDH, bilirubin, reticulocytes, and RDW—“were all trending in the right direction,” which he said supported the conclusion of less hemolysis. He added that the resulting increase in total hemoglobin should help patient fatigue.

SVP of Clinical Development Iain Fraser and Sapir also discussed a VOC reduction trend observed in the 12-week dataset. Schwartz noted that PIONEER saw six VOCs versus 16 expected over 12 weeks. Fraser said seven of the 12 patients had no VOC during the treatment period and argued that the signal was notable because HbF was still rising during the 12 weeks and patients had not yet reached a steady-state maximal effect.

How the company is thinking about responders and variability

Schwartz asked about the roughly 40% of patients who did not reach HbF levels of at least 20%. Sapir said every evaluated patient saw an HbF increase and that, on average, all 12 patients had at least a 6.5% absolute increase. He cited an example of a patient who started at 1.5% HbF and reached 9% by study end, arguing that even without reaching 20%, the magnitude of the increase could be clinically meaningful.

Fulcrum also discussed post hoc observations around response variability. Fraser said that within the 12-milligram cohort (16 evaluable patients), all patients increased HbF, but a couple had less robust responses. Some of that, he said, was related to multiple blood transfusions, which can depress measured HbF by diluting it with normal hemoglobin. He added that several lower baseline and lower response patients came from a site in South Africa, and that those patients originated from the Democratic Republic of Congo, where a sickle cell haplotype (CAR/Bantu) is associated with low baseline HbF, severe disease, and lower responsiveness to hydroxyurea. Fraser said the company did not yet have DNA sequencing to confirm haplotype status but was investigating the association.

In the 20-mg dose group, Fraser said the same magnitude of geography-related effect was not seen, noting that only one patient in that cohort came from the South African site and that additional patients were enrolled from Nigeria, which he said is expected to be more heterogeneous and more similar to the U.S. population. He said geography could become an important stratification factor in a pivotal study to avoid imbalances in responsiveness between treatment and placebo arms.

Schwartz also asked about one patient whose HbF declined from 34% to 29%. Fraser said the observation was anomalous, that the company had not identified a specific cause after reviewing labs, and that the team believed it was likely assay variability. He added that the patient’s baseline was 8% and ending at 29% remained a strong outcome.

Safety discussion: reticulocytes, hemoglobin, and cytopenias

On hematologic safety, Fraser described two categories of evidence. On the red cell side, he said reticulocytes decreased as expected with treatment, reflecting less bone marrow stress, while total hemoglobin increased—an observation he argued would be inconsistent with bone marrow suppression. Fraser said the data aligned with the hypothesis that higher HbF makes red cells less prone to hemolyze, extending their survival and raising total hemoglobin.

For other blood cell lineages, Fraser said the company has not seen cytopenias except for one disclosed case in the 20-mg cohort, which occurred in the setting of an upper respiratory tract infection and a positive test for parvovirus B19. He said the drug was held and counts recovered after treatment was restarted, and that the reticulocyte trend did not return to baseline, which he described as consistent with therapeutic effect.

Regulatory strategy: registrational study and potential accelerated approval

Sapir said Fulcrum has an upcoming end-of-phase meeting with the FDA and expects to share guidance from that interaction in the second quarter. He said the company plans to propose a registrational study as the next trial in a more severe sickle cell population, and that if the FDA agrees, the company would aim to start it in the second half of the year.

He described a trial likely in the range of 200–300 patients with VOCs assessed at the one-year mark, similar to other programs. Sapir said Fulcrum also intends to propose an interim analysis within the same study: assessing HbF at six months in a subset of patients (roughly half of the total). If successful, Sapir said the company would seek accelerated approval at that point.

Fraser discussed powering considerations, including being cautious about placebo-group VOC rate assumptions, dispersion (variability) of VOCs, and effect size. He also said dropout assumptions are a key factor, and referenced using a conservative dropout rate “in the 30% dropout range” to provide cushion for the VOC endpoint.

Other topics: label considerations, PRC2 read-through, focus and pipeline

On how enrollment criteria might translate to a future label, Sapir said Fulcrum is targeting a severe patient population—an approach he said enriches for higher VOC rates and improves powering and the probability of success. He estimated the company’s current inclusion/exclusion criteria represent roughly 20% of the overall population, but he argued that VOC thresholds used for trial entry in other therapies have differed and were not reflected in their eventual indication statements, which he characterized as referencing “severe sickle cell disease” or “recurrent VOEs.”

Sapir addressed investor questions stemming from Ipsen’s announcement that it would stop development and promotion of tazemetostat (Tazverik), a PRC2 inhibitor, in follicular lymphoma. Sapir emphasized that Fulcrum’s program and tazemetostat target different components of PRC2—tazemetostat targets EZH2, while Fulcrum targets EED—and said risk-benefit assessments are disease-specific, arguing that conclusions in a cancer indication may not generalize to sickle cell disease.

On commercialization and partnering, Sapir said the company believes the greatest shareholder return comes from approving the drug as quickly as possible and commercializing it in the U.S. He said Fulcrum is about 50 people and suggested ex-U.S. commercialization—particularly in Europe—could be too resource-intensive, making an ex-U.S. partnership more likely while retaining U.S. commercialization.

Sapir also said that with cash runway into 2029, the company is funded through its first pivotal readout and expects near-term focus (18–24 months) to be centered on regulatory interactions and initiating and enrolling the registrational study. Longer-term, he said Fulcrum has ambitions to become a “world-class benign heme company” through discovery and potential in-licensing over the next five years.

Finally, Sapir said Fulcrum has discontinued its Diamond-Blackfan anemia (DBA) program. He said the company was working toward an IND but determined during IND-enabling work that it would not meet a rigorous target product profile, prompting a refocus of resources on the sickle cell program.

About Fulcrum Therapeutics (NASDAQ:FULC)

Fulcrum Therapeutics, Inc is a clinical-stage biopharmaceutical company focused on discovering and developing precision medicines that modulate gene expression through epigenetic control. Leveraging a proprietary target discovery platform, Fulcrum seeks to identify small‐molecule therapeutics that restore normal gene function in diseases caused by genetic dysregulation. The company’s core research efforts center on transcriptional regulators and chromatin-modifying proteins, aiming to address underlying disease mechanisms rather than downstream symptoms.

Fulcrum’s most advanced programs include FTX-6058, an oral therapeutic candidate designed to elevate fetal hemoglobin levels in patients with sickle cell disease and beta-thalassemia, and a preclinical program targeting facioscapulohumeral muscular dystrophy (FSHD) by inhibiting a key epigenetic driver of aberrant gene expression.