Tazemetostat for Mesothelioma

Tazemetostat Treatment Profile
Selective Oral EZH2 Inhibitor (Investigational in Mesothelioma)
Category	Medical / Treatment
Drug Class	EZH2 methyltransferase inhibitor
Tumor Target	BAP1-inactivated tumor cells
Pivotal Study	Phase 2, single-arm (NCT02860286)
Trial Status	Completed
Week-12 Disease Control	54% (33 of 61)
Complete Responses	0
FDA Status (Mesothelioma)	Not approved — investigational

Executive Summary

Tazemetostat is an investigational oral EZH2 inhibitor studied for BAP1-inactivated pleural mesothelioma, a cancer caused by asbestos exposure. In a completed, single-arm phase 2 trial (NCT02860286), it produced a 54% disease control rate at week 12 (33 of 61 patients), with no complete responses. It is not FDA-approved for mesothelioma and remains research-stage; patients access it only through clinical trials, which typically require confirmation that the tumor has lost BAP1 function.

Tazemetostat (brand name Tazverik) is a selective, oral inhibitor of EZH2, an enzyme that many mesothelioma tumors depend on for survival. It has been studied in malignant pleural mesothelioma as a targeted therapy aimed at tumors whose cells have lost the function of the BAP1 gene. In a completed, single-arm phase 2 study of relapsed or refractory, BAP1-inactivated pleural mesothelioma, tazemetostat produced a disease control rate of 54% at week 12 — meaning about half of evaluable patients had their disease either shrink or stop growing at that timepoint.

Mesothelioma is caused by asbestos exposure. Within the resulting tumor cells, the BAP1 gene is frequently inactivated — a somatic (acquired) alteration present in the cancer itself, not an inherited trait — and this tumor change is precisely what tazemetostat is designed to exploit. When BAP1 is lost inside a tumor cell, that cell becomes unusually dependent on EZH2 activity, a relationship scientists call synthetic lethality. Blocking EZH2 with tazemetostat is intended to selectively stress cancer cells carrying that vulnerability.

The evidence for tazemetostat in mesothelioma comes from a single-arm phase 2 trial, not a randomized comparison against another treatment. The study measured disease control, not overall survival, and it recorded no confirmed complete responses. Tazemetostat is FDA-approved for other cancers but is not approved for mesothelioma — in mesothelioma it remains an investigational, research-stage option. Patients interested in EZH2-directed treatment would generally need to access it through a clinical trial.

At-a-Glance

Tazemetostat for mesothelioma at a glance:

• Tazemetostat targets a vulnerability created inside the tumor by BAP1 loss — BAP1 inactivation is the single most common molecular alteration in pleural mesothelioma cells and leaves them dependent on the EZH2 enzyme
• About half of evaluable patients had disease control at week 12 — the phase 2 trial reported a 54% disease control rate (33 of 61 patients; 95% CI 42–67)
• No patient achieved a complete response — only two confirmed partial responses were recorded, lasting 18 and 42 weeks
• The trial was single-arm, not randomized — there was no comparator group, so the results cannot be read as a survival benefit over chemotherapy or immunotherapy
• Nearly every enrolled patient had a BAP1-inactivated tumor — 73 of 74 participants (99%) had confirmed loss of BAP1 function in their cancer, the biomarker the drug is built around
• Tazemetostat is taken by mouth — it is an oral EZH2 inhibitor, distinct from intravenous chemotherapy or checkpoint immunotherapy
• Serious side effects occurred in about one-third of patients — grade 3–4 events included hyperglycemia (7%), hyponatremia (7%), and anemia (5%); no deaths on study were treatment-related
• The pivotal trial is completed — NCT02860286 is registered as "Completed," so these figures reflect a finished study rather than a preliminary look
• It is not FDA-approved for mesothelioma — tazemetostat is approved for epithelioid sarcoma and follicular lymphoma, but its mesothelioma use is investigational only
• Laboratory research continues to refine who benefits — genetic screens and pathway studies are still mapping how BAP1 loss and EZH2 dependence interact in mesothelioma

Key Facts

Measure	Finding (Source)
Drug and Class	Tazemetostat, a selective oral enhancer of zeste homolog 2 (EZH2) methyltransferase inhibitor
Tumor Biomarker	BAP1-inactivated tumor cells — a somatic alteration and the most common molecular change in pleural mesothelioma
Trial Design	Multicentre, open-label, single-arm, two-part phase 2 study; 74 enrolled (Zauderer et al., Lancet Oncology 2022)
Primary Endpoint	Disease control rate (complete response + partial response + stable disease) at week 12 — not overall survival
Week-12 Disease Control Rate	54% (33 of 61 evaluable patients; 95% CI 42–67)
Objective Responses	0 complete responses; 2 confirmed partial responses (durations 18 and 42 weeks)
Grade 3–4 Adverse Events	Hyperglycemia 7%, hyponatremia 7%, anemia 5%; serious adverse events in 34% (25 of 74); no treatment-related deaths
Registry Status	NCT02860286 — "Completed," phase 2, sponsored by Epizyme
FDA Status in Mesothelioma	Not approved for mesothelioma; approved for epithelioid sarcoma and follicular lymphoma
Route of Administration	Oral

How does BAP1 loss create a treatment target in mesothelioma?

Asbestos exposure is the established cause of malignant pleural mesothelioma. As the disease develops, the tumor cells accumulate molecular changes, and the most frequent of these is inactivation of the BAP1 gene. This is a somatic event — an alteration acquired by the cancer cells themselves — and it can be detected in tumor tissue by immunohistochemistry (loss of nuclear BAP1 staining) or by sequencing. Because BAP1 loss is so common in mesothelioma tumors, it has become one of the most studied handles for designing targeted treatment.

BAP1 normally works as a tumor-suppressor and helps regulate how genes are switched on and off. When its function is lost inside a tumor cell, the enzyme EZH2 — which silences genes by adding methyl marks to chromatin — becomes over-active, and the cell grows increasingly dependent on that EZH2 activity to survive. Researchers describe this as a synthetic-lethal relationship: neither BAP1 loss nor EZH2 inhibition alone is uniformly fatal to the cell, but combining the pre-existing BAP1 loss with a drug that blocks EZH2 selectively stresses the cancer. Tazemetostat is the EZH2 inhibitor tested against this vulnerability.

Laboratory work continues to characterize this dependency. Genome-wide genetic screens in BAP1-deficient mesothelioma models have confirmed EZH2 among the targetable vulnerabilities that emerge when BAP1 is lost, and pathway studies are mapping how the BAP1–EZH2 axis behaves across cancer types. Importantly, this is tumor biology aimed at treatment — it describes a weakness inside cancer that already exists, not a change in what causes mesothelioma. The cause remains asbestos.

What did the phase 2 tazemetostat trial find?

The clinical evidence comes from a multicentre, open-label, two-part phase 2 study (NCT02860286) led by Zauderer and colleagues and published in The Lancet Oncology in 2022. Part 1 assessed pharmacokinetics in 13 patients; Part 2 evaluated efficacy in patients with relapsed or refractory pleural mesothelioma whose tumors were BAP1-inactivated. Across the study, 74 patients were enrolled, and 73 of them (99%) had confirmed loss of BAP1 function in their cancer.

The primary endpoint of Part 2 was the disease control rate — the share of patients with a complete response, partial response, or stable disease — measured at week 12. Among the 61 efficacy-evaluable patients, the disease control rate was 54% (33 patients; 95% CI 42–67). There were no confirmed complete responses, and only two confirmed partial responses, which lasted 18 and 42 weeks. Because the trial had a single arm and no comparator, these figures describe activity in a biomarker-selected group rather than a proven advantage over standard chemotherapy or immunotherapy, and disease control at a single timepoint is not the same as a documented survival benefit.

This is a meaningful but early signal. It is stronger than a first-in-human safety readout because it is a completed phase 2 study with a defined efficacy endpoint, yet it stops well short of the randomized, survival-based evidence that supports approved mesothelioma regimens such as first-line immunotherapy.

How well tolerated is tazemetostat in mesothelioma?

Tolerability in the trial was consistent with tazemetostat's known profile as an oral EZH2 inhibitor. Grade 3–4 treatment-emergent adverse events were relatively uncommon and included hyperglycemia (7%), hyponatremia (7%), and anemia (5%). Serious adverse events of any cause occurred in 34% of patients (25 of 74). Five deaths occurred on study, but none were considered treatment-related.

For patients, the oral route and generally manageable side-effect profile are part of why EZH2 inhibition has drawn interest as a possible option for a molecularly defined subgroup. Any patient considering tazemetostat should discuss the full risk–benefit picture — including that its mesothelioma use is investigational — with their treating oncologist.

Is tazemetostat approved for mesothelioma?

No. Tazemetostat is not FDA-approved for mesothelioma. It is approved in the United States for other cancers — metastatic or locally advanced epithelioid sarcoma, and relapsed or refractory follicular lymphoma in defined settings — but mesothelioma is not among its approved indications. In mesothelioma, tazemetostat has been evaluated only in the research setting, and the phase 2 trial that generated its mesothelioma data is now complete.

Practically, this means EZH2-directed therapy is not a standard-of-care option a patient can simply be prescribed for mesothelioma today. Access generally comes through clinical trials, and eligibility usually depends on confirming that the tumor is BAP1-inactivated. Patients and families weighing options can review current studies through mesothelioma clinical trials resources and discuss molecular testing with their care team.

What does EZH2 inhibition mean for mesothelioma patients today?

The honest framing is that tazemetostat represents a promising, biomarker-driven research direction — not an established treatment. Its main value right now is what it demonstrates about mesothelioma biology: that a very common tumor alteration (BAP1 loss) creates a specific vulnerability (EZH2 dependence) that a targeted drug can act on. The phase 2 disease-control signal supports continued investigation, while the absence of complete responses and of randomized survival data keeps expectations grounded.

For patients, three points matter most. First, molecular testing of the tumor — including BAP1 status — is what identifies whether an EZH2-directed trial is even relevant, which is why molecular and genetic testing is increasingly part of the mesothelioma workup. Second, disease control means slowing or stabilizing the cancer for some patients, not curing it. Third, established options — including immunotherapy and other approaches summarized under latest treatment advances — remain the backbone of care while targeted strategies like this one are studied further.

Is tazemetostat a form of chemotherapy?

No. Tazemetostat is a targeted therapy, not chemotherapy. Chemotherapy broadly attacks rapidly dividing cells, whereas tazemetostat is an oral small molecule that specifically inhibits the EZH2 enzyme, aiming at the vulnerability created by BAP1 loss inside mesothelioma tumor cells. In the mesothelioma trial it was studied as a single agent in patients whose disease had relapsed or was refractory to prior treatment.

Does every mesothelioma patient qualify for EZH2-targeted therapy?

No. The approach is specific to tumors that are BAP1-inactivated, which is why the trial confirmed BAP1 status in nearly all enrolled patients. A patient's suitability depends on molecular testing of the tumor and on the availability of an open clinical trial, since tazemetostat is investigational in mesothelioma. Not all mesotheliomas carry the same alterations, and BAP1 testing is what distinguishes candidates from non-candidates for this particular strategy.

How is tazemetostat different from immunotherapy for mesothelioma?

They work in fundamentally different ways. Immunotherapy — the FDA-approved nivolumab-plus-ipilimumab combination — releases brakes on the immune system so T cells can attack tumor cells, and it is supported by randomized survival data. Tazemetostat instead acts directly on a molecular dependency (EZH2) inside BAP1-inactivated tumor cells and is supported only by single-arm, disease-control data. Immunotherapy is standard first-line care; EZH2 inhibition is investigational and biomarker-restricted.

Related Pages

• Immunotherapy for Mesothelioma
• Latest Treatment Advances for Mesothelioma
• Clinical Trials for Mesothelioma
• Mesothelioma Molecular and Genetic Testing
• Histological Subtypes of Mesothelioma
• Mesothelioma Treatment Overview

External Links

• Danziger & De Llano — Mesothelioma Treatment and Legal Resources — overview of mesothelioma treatment options and the compensation process for patients and families
• Mesothelioma Lawyers Near Me — patient guides, treatment explainers, and attorney directory
• Mesothelioma.net — patient resources on diagnosis, treatment, and clinical trials

Patient advocacy and support for mesothelioma families is provided by David Foster, a Patient Advocate at Danziger & De Llano.