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Prostate Cancer Treatment and Research / Epigenetics and DNA Methylation · Journal article
Clinical Cancer Research · August 14, 2026
An action by a regulator. Authoritative on labelling and availability.
In March 2026, Ipsen voluntarily withdrew tazemetostat (an EZH2 inhibitor) from all markets following SYMPHONY-1 trial results showing hematologic second primary malignancies in 5.7% of treated patients versus none in controls, predominantly myelodysplastic syndrome and acute myeloid leukemia. The authors argue this reflects on-target biology: EZH2 loss impairs hematopoietic stem cell differentiation and is recurrent in myeloid malignancies, suggesting the risk may extend to other EZH2 inhibitors and indications with prolonged exposure, particularly in ongoing prostate cancer programs.
Phase Ib/III randomized controlled trial (SYMPHONY-1). Patients enrolled in SYMPHONY-1 Phase Ib/III trial; exact disease/indication and demographics not specified in the source text.. Intervention: Tazemetostat (EZH2 inhibitor). Compared with: Control (unspecified).
Hematologic second primary malignancies occurred in 5.7% of tazemetostat-treated patients in SYMPHONY-1 trial No hematologic SPMs reported in control arm of SYMPHONY-1 Most frequent SPMs were myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML)
Safety was not reported in the material analysed. Check the source before drawing any conclusion about harm.
Clinicians should be aware that EZH2 inhibition carries a target-mediated risk of myeloid neoplasia that may be class-wide rather than agent-specific. This finding argues for heightened pharmacovigilance and reassessment of risk–benefit in ongoing EZH2 inhibitor trials, particularly in indications requiring prolonged exposure.
A regulator-initiated market withdrawal based on confirmatory Phase Ib/III trial data showing a clinically significant safety signal (hematologic SPMs) that changes the risk–benefit profile of an approved agent.
As stated by the source record.
Quoted from the source exactly as published.
Clinicians should be aware that EZH2 inhibition carries a target-mediated risk of myeloid neoplasia that may be class-wide rather than agent-specific. This finding argues for heightened pharmacovigilance and reassessment of risk–benefit in ongoing EZH2 inhibitor trials, particularly in indications requiring prolonged exposure.
Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.
In March 2026, Ipsen voluntarily withdrew the EZH2 inhibitor tazemetostat (Tazverik) from all markets and indications following results from the confirmatory Phase Ib/III SYMPHONY-1 trial demonstrating hematologic second primary malignancies (SPMs) in 5.7% of treated patients, compared with none in the control arm. The most frequently reported SPMs were myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Although this finding may be interpreted as an idiosyncratic liability of a single agent, the biology of EZH2 suggests a broader, target-driven risk. EZH2 functions in a context-dependent manner as both an oncogene and a tumor suppressor. Gain-of-function mutations drive transformation in germinal center B-cell lymphomas, whereas loss-of-function alterations impair hematopoietic stem cell differentiation and are recurrent in myeloid malignancies, including MDS and AML. In selected solid tumor contexts, such as specific subtypes of medulloblastoma, EZH2 loss can likewise promote tumorigenesis. These observations raise concern that chronic pharmacologic inhibition of EZH2 may phenocopy loss-of-function states that initiate myeloid neoplasia. We argue that the withdrawal of tazemetostat exposes a fundamental vulnerability in the development of epigenetic therapies: target validation has focused on tumor-intrinsic effects while underweighting consequences in normal stem cell compartments. This issue is particularly relevant for ongoing Phase III programs in prostate cancer, where prolonged exposure may amplify latency-dependent risks. We propose changes to preclinical safety assessment, trial design, and pharmacovigilance to mitigate predictable, target-mediated toxicities.
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