Intravesical Oncolytic Immunotherapy Produces Complete Tumor Regression in Three-Quarters of Patients in Phase 3 Trial

After their disease stops responding to Bacillus Calmette-Guérin (BCG) therapy, patients with high-risk non-muscle-invasive bladder cancer often face the difficult choice of having their bladder removed. An international Phase 3 trial showed that cretostimogene grenadenorepvec, an oncolytic immunotherapy administered directly into the bladder, could produce complete tumor regression in about three-quarters of evaluable patients, with some responses lasting more than two years.

BOND-003 Cohort C enrolled 115 people at 41 centers, of whom 112 received treatment and 110 were available for the primary efficacy analysis. After a median follow-up of 25.8 months, 83 people achieved a complete response confirmed by central review, equivalent to 75.5%; the paper reported the statistical result as 75%, with a 95% confidence interval of 66.3% to 83.2%. All participants had high-risk, BCG-unresponsive non-muscle-invasive bladder cancer with carcinoma in situ.

The therapy is a modified adenovirus that is instilled into the bladder through a catheter and designed to replicate selectively inside cancer cells, destroy tumors, and stimulate a local immune response. Its clinical significance lies not only in whether tumors disappear temporarily, but also in whether it can delay recurrence and radical cystectomy, avoiding the long-term effects of surgery on urinary function, quality of life, and physical function.

An extended analysis released by the research team estimated that about 60% of complete responders remained recurrence-free after two years, with the longest response lasting more than four years; about 81% of all patients had not undergone cystectomy two years after starting treatment. However, these are time-to-event estimates and cannot be interpreted to mean that every patient can preserve their bladder over the long term. They are also not sufficient to prove that delaying surgery will not affect subsequent cancer control.

Regarding safety, the study recorded no Grade 3 or Grade 4 treatment-related adverse events and no cases of treatment discontinuation or death due to treatment side effects; two patients experienced serious but Grade 2 treatment-related events. These results support the tolerability of intravesical administration, but a study of 115 people remains too small to rule out rare or later-emerging risks.

The most important limitation is that BOND-003 used a single-arm design and did not randomly compare cretostimogene with other bladder-preserving therapies or cystectomy. It therefore cannot establish whether response rates, survival outcomes, or quality of life are better than with existing options. The therapy remains investigational; the study was funded by its developer, CG Oncology, and the paper also disclosed relationships between multiple researchers and the sponsor and other pharmaceutical companies. These data provide substantial evidence supporting the possibility of avoiding bladder removal, but they are not yet the final answer on the relative merits of different treatment strategies.