Phase 3 Trial Confirms Viral Immunotherapy CAN-2409 Plus Radiation Improves Disease-Free Survival in Localized Prostate Cancer

A new viral immunotherapy has made a strong case to become the first new treatment option in over two decades for men with intermediate-to-high-risk localized prostate cancer. In a pivotal Phase 3 trial, adding aglatimagene besadenovec (CAN-2409) to standard radiation therapy significantly delayed cancer recurrence, with a safety profile that did not add serious toxicity to existing treatments. The results, published in The Lancet Oncology, mark a major step toward regulatory approval.

How the Phase 3 Trial Was Designed

The pivotal Phase 3 trial (NCT01436968) was a multicenter, randomized, double-blind, placebo-controlled study. It enrolled 745 patients with newly diagnosed, intermediate-to-high-risk localized prostate cancer . Participants were randomized in a 2:1 ratio to receive either aglatimagene besadenovec plus valacyclovir or a placebo plus valacyclovir, with both groups receiving standard-of-care radiotherapy, with or without a short course of androgen deprivation therapy .

Key Efficacy Results: Improving Over Time

The trial met its primary endpoint, demonstrating a statistically significant improvement in disease-free survival (DFS).

Initial Analysis (Median 50.3-Month Follow-up):

• The median DFS in the aglatimagene group was not reached, meaning the majority of patients had not yet experienced a recurrence event, compared to 86.1 months in the placebo group .
• This translated to a hazard ratio of 0.70 (95% CI 0.52–0.94; p=0.016), representing a 30% reduction in the risk of recurrence or death from any cause .

Extended Follow-up (Median 58 Months, Reported at AUA 2026):
The benefit appeared to deepen with more time. In a follow-up analysis presented 20 months after the initial topline data, the impact on prostate cancer-specific outcomes was even more pronounced .

• The improvement in prostate cancer-specific DFS reached 39% (hazard ratio 0.61; 95% CI 0.44–0.85; p=0.0031) .

Secondary Endpoints Add Further Support:
A landmark secondary endpoint focused on tumor eradication at one year. The rate of negative biopsies at 2 years was 80% in the aglatimagene arm compared to 63% in the placebo arm (p=0.0018) . This benefit was consistent whether patients received conventional or moderately hypofractionated radiotherapy .

It is important to note that while the results are strongly positive for the overall study population, the trial was not statistically powered to definitively prove a benefit within any one specific patient subgroup .

A Manageable Safety Profile

The addition of aglatimagene to radiotherapy did not cause a significant increase in severe toxicity . The safety profile was generally favorable and manageable .

Most side effects were mild and temporary. The most common treatment-related adverse events were flu-like symptoms and local reactions :

• Chills (33.4% vs. 8.6% for placebo)
• Flu-like symptoms (30.5% vs. 13.8%)
• Fever (25.1% vs. 3.9%)
• Fatigue (18.2%)
• Urinary frequency (12.1%)

The rates of treatment-related serious adverse events were low and similar between the two groups . No new safety signals were identified in a pooled safety analysis of the product's use .

How CAN-2409 Works: Turning a Tumor Into a Vaccine

Aglatimagene besadenovec (CAN-2409) is an investigational, off-the-shelf therapy that combines gene therapy and immunotherapy using a three-step mechanism .

1. Gene Delivery: The therapy consists of a replication-defective adenovirus engineered to carry the herpes simplex virus thymidine kinase (HSV-tk) gene. It is injected directly into the tumor, where it infects cancer cells to deliver the gene with minimal systemic impact .
2. Prodrug Activation: Patients then take an oral prodrug called valacyclovir, a widely available antiviral medication. Inside the cancer cells that received the gene, the HSV-tk enzyme converts this harmless prodrug into a toxic metabolite that selectively disrupts DNA replication, causing the engineered cancer cells to die .
3. Immune System Activation: This targeted cell death is "immunogenic," meaning it releases a flood of tumor-specific antigens. This debris acts as a danger signal, educating and activating the patient’s own immune system to seek out and destroy remaining cancer cells throughout the body. This process, which turns the patient's own tumor into an in-situ personalized cancer vaccine, is further enhanced by the DNA damage caused by concurrent radiation therapy .

This multimodal attack delivers a direct hit to the injected tumor while simultaneously marshaling the body's defenses for a systemic and potentially long-lasting anti-tumor response.

The Path to a Potential Approval in Q4 2026

The positive data have paved a clear regulatory path for Candel Therapeutics, which has consistently stated its intention to seek U.S. approval.

• BLA Submission: The company plans to submit a Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) for aglatimagene in localized, intermediate-to-high-risk prostate cancer in the fourth quarter of 2026 .
• Regulatory Momentum: CAN-2409 has already received the FDA's Regenerative Medicine Advanced Therapy (RMAT) designation for this indication, which provides a pathway for expedited development and review .
• Peer-Reviewed Validation: The full Phase 3 results were published in The Lancet Oncology in June 2026, providing a high-impact, peer-reviewed foundation that strengthens the case for regulatory discussions .
• Manufacturing Status: Because it is manufactured in advance and does not require personalization for each patient, aglatimagene is considered an "off-the-shelf" product, which simplifies manufacturing and logistics .

Beyond prostate cancer, CAN-2409 is being evaluated in clinical trials for other hard-to-treat solid tumors, including pancreatic cancer and non-small cell lung cancer (NSCLC), though the prostate cancer program is the most advanced and the lead indication for commercialization .