enGene Therapeutics reported updated results from the pivotal cohort of its Phase 2 LEGEND trial on Nov. 11, saying its non-viral gene therapy detalimogene produced a complete response in 56% of evaluable patients with high-risk, BCG-unresponsive non-muscle invasive bladder cancer. The landmark 12-month complete response rate was 24%, and the preliminary estimate of durable response lasting at least 12 months was 43%. The company said it plans to initiate a Biologics License Application by the end of 2026, with potential FDA approval in 2027.
The data, presented in a press release and discussed on a conference call, are the most mature look yet at a therapy that would be the first non-viral plasmid gene therapy approved for this indication. They also come with the caveats of a single-arm, open-label trial: there is no control group, the confidence intervals are wide, and the follow-up is still maturing. The company has not reported overall survival or progression-free survival data, which are the outcomes that would matter most in a larger, longer study. But the direction of the data matters. The 12-month response rate rose from 13% in an earlier analysis to 24%, and the median duration of response rose from 8.6 months to 10.1 months.
The disease
Non-muscle invasive bladder cancer accounts for about 75% to 80% of new bladder cancer diagnoses. It grows in the tissue lining the bladder but has not reached the muscle wall. It can appear as papillary growths, which are typically removed, or as carcinoma in situ, flat lesions that are difficult to resect. The two forms can occur together.
The standard first treatment is BCG, a bacteria-based immunotherapy instilled into the bladder. Many patients respond, but some do not. High-risk patients who are unresponsive to BCG face recurrence rates of 50% to 70%, and the next step is often cystectomy, the removal of the bladder. That is a curative operation, but it changes how a person urinates and carries significant quality-of-life consequences. New bladder-preserving options have been approved in recent years, but the need is far from met.
The economics are part of the problem. NMIBC requires repeated cystoscopies, treatments, and follow-up, and it is one of the most expensive cancers to manage over time. Cystectomy is costly and life-altering, but so is a therapy that fails and leads to surgery anyway. A bladder-preserving treatment that keeps patients in response for a year or more could reduce both the clinical burden and the total cost, which is why payers will look closely at the durability data.
BCG supply has also been a recurring problem. The global shortage of BCG has forced clinics to ration doses and delay treatment, which can complicate care for patients who need it. A therapy that does not depend on the BCG supply chain has an obvious appeal, though detalimogene is designed for patients who have already failed BCG, not as a replacement for it.
The data
The LEGEND trial's pivotal cohort enrolled 125 patients with high-risk, BCG-unresponsive NMIBC with carcinoma in situ, with or without papillary disease. The efficacy analysis included 120 evaluable patients as of an Oct. 29 data cutoff, according to the company's release. The 56% complete response rate at any time has a 95% confidence interval of 47% to 65%. The 24% landmark 12-month response rate included 110 patients, with one assessment pending.
The duration data are still maturing. Median follow-up for responders was 12.0 months, up from 9.2 months in April. Nine patients were pending the 12-month durability assessment, and eight patients in maintenance were awaiting an assessment. The company said every patient who entered maintenance and had been assessed for durability had a durable response, which is encouraging but based on a small number of events.
The progression data are the strongest part of the package. The company said 97% of all efficacy-evaluable patients were free from progression to muscle-invasive or metastatic disease, and 100% of responders were free from progression to T2 or greater disease in the bladder. About 86% of all patients remained free from cystectomy, and 96% of responders did. Those numbers are the ones that matter most to patients deciding between a bladder-preserving therapy and surgery.
The trial is open-label and single-arm, which limits what the data can prove. There is no randomized comparison to BCG, to cystectomy, or to another bladder-preserving therapy. Response is assessed by cystoscopy and biopsy, and the definition of complete response in NMIBC is well established, but the absence of a control group means the results must be compared with historical data and with other single-arm trials. The FDA has accepted that kind of evidence for this indication before, which is why the company is moving to a BLA.
Safety looked manageable. Of 125 patients, 59% had at least one treatment-related adverse event, mostly Grade 1 or 2. The most common were fatigue (21%), painful urination (16%), frequent urination (16%), bladder spasm (13%), urgency (13%), and urinary tract infection (10%). Grade 3 events occurred in 4%, serious events in 2%, and there were no Grade 4 or 5 events. About 1% of patients discontinued treatment because of an adverse event.
The therapy
Detalimogene is a non-viral gene therapy designed to be instilled into the bladder, where it is intended to produce a localized anti-tumor immune response. It uses enGene's Dually Derivatized Oligochitosan, or DDX, platform, which the company says can overcome some limits of viral gene therapies, including complicated handling and cold-chain requirements.
That delivery advantage is central to the commercial case. Most bladder cancer care happens in community urology practices, not academic centers. A therapy that is easier to store, prepare, and administer could fit more easily into those settings. The company says more than 75% of high-risk, BCG-unresponsive NMIBC patients receive care in community urology.
The regulatory path
Detalimogene has FDA Regenerative Medicine Advanced Therapy and Fast Track designations and was selected for the agency's CMC Development and Readiness Pilot, which is designed to help manufacturers prepare for compressed review timelines. After a pre-BLA meeting, enGene said it aligned with the FDA on key components of the application, including the efficacy-evaluable population.
The company plans to initiate the BLA submission by year-end, complete it in the first half of 2027, and launch in 2027 if approved. The application will rest on the single pivotal cohort, a path the FDA has accepted for other bladder-preserving therapies but one that puts pressure on the durability data. The agency will review the manufacturing process, the safety database, and the strength of the response evidence.
LEGEND has other cohorts that could expand the label later. Cohort 2a enrolls patients with CIS who have not received BCG, and the company expects an update on a detalimogene plus surfactant bladder rinse cohort in mid-2027. Those data are not part of the initial BLA, but they could support broader use if the first approval holds.
The competition
The bladder-preserving market has changed quickly. Adstiladrin, a viral gene therapy from Ferring, was approved in 2022 for BCG-unresponsive carcinoma in situ. ANKTIVA, an IL-15 receptor agonist from ImmunityBio, was approved in 2024 and is given with BCG; the company has also reported data in BCG-naive patients. Keytruda, Merck's PD-1 inhibitor, has an accelerated approval in BCG-unresponsive high-risk NMIBC.
Detalimogene would enter that market with a different delivery technology and a claim of easier handling. The company argues its efficacy is now within range of approved products, though cross-trial comparisons are unreliable because the trials differ in design, patient mix, and response definitions. The more meaningful test will be how the FDA views the single-arm data and how urologists weigh the convenience of a non-viral product against the durability of its response.
What to watch
The BLA submission is the next milestone. Watch whether enGene initiates it by year-end and whether the FDA accepts the application for review. The durability data will mature during the review, and any updates on the 12-month response rate and cystectomy-free survival will matter. The safety database will also grow as more patients are treated.
The commercial question is separate. A 2027 launch would put detalimogene into a market where Adstiladrin, ANKTIVA, and Keytruda already have relationships with urologists. The company's bet is that community practices want a therapy that is easier to use and does not require the cold-chain and handling steps of viral gene therapies. That bet will be tested in the first year of sales.
For patients, the near-term change is not a new option yet. It is the prospect of one. The data are encouraging, and the cystectomy-sparing numbers are the ones that will drive interest. But the therapy still has to clear the FDA, and the durability data still have to hold. The BLA will show whether regulators think the evidence is enough.
The decision for a patient is not abstract. A complete response means the cancer is no longer visible on cystoscopy and biopsy. It does not mean the cancer is gone forever, and it does not remove the need for surveillance. But for someone facing bladder removal, a year or more of response can be the difference between keeping the bladder and losing it. That is the outcome the trial is trying to measure, and the outcome the company will emphasize in its FDA submission.
Primary sources
- enGene's Nov. 11 press release for the LEGEND Cohort 1 efficacy and safety data, the regulatory designations, the BLA timeline, and the company and investigator statements.
- Business Wire's copy of the same release for the detailed response and safety tables.
- Mavengity's Nov. 9 ANKTIVA article for the BCG-naive NMIBC context.