Adding Gene Therapy Injections to Radiation Kept Prostate Cancer Away Longer

CATEGORY: MEN’S HEALTH

Can a prostate tumor be turned into its own vaccine? That question drove a phase 3 trial of CAN-2409, a gene therapy injected directly into the prostate while men underwent standard radiation for localized prostate cancer. Among 745 men followed for a median of just over four years, adding the injections cut the risk of recurrence or death by 30% compared with placebo.¹ The therapy isn’t approved yet.

Three Injections, an Antiviral Pill, and an Alerted Immune System

CAN-2409, generic name aglatimagene besadenovec, uses a disabled cold virus as a courier. Doctors inject it into the prostate in three courses, each paired with valacyclovir, an ordinary antiviral pill long used for herpes and shingles. Inside the injected cells, and only there, a delivered gene converts the pill into a cell-killing compound. Dying tumor cells then spill their contents where immune cells can inspect them. The hoped-for result is a vaccine made on site. Its recipe is the man’s own cancer. The trial enrolled men with intermediate- or high-risk cancer still confined to the prostate at 51 US centers. All received radiation with curative intent, and about half of each group also had short-term hormone therapy. A blinded two-to-one draw gave 496 men the gene therapy and 249 placebo injections.¹

Fewer Recurrences and Cleaner Biopsies at Two Years

Over a median follow-up of 50 months, men on the gene therapy were 30% less likely to see their disease return or to die. Half the placebo group had such an event by 86 months, while the treated group never reached that halfway point. Counting only prostate cancer events, the risk ran 38% lower. Among men biopsied about two years after radiation, 80% on the therapy had no cancer in the sample, versus 63% on placebo.¹ Those biopsies covered 451 of the 745 men, so they carry less weight than the main result.

Mild Side Effects, and the Question Time Hasn’t Answered

Severe side effects were about as common with the therapy as without it: 8% versus 7%. Chills, flu-like symptoms, fatigue and fever led the list, mostly brief and mild, and no deaths were tied to treatment.¹ What hasn’t appeared is a survival difference. Deaths were few in both groups, leaving that comparison wide open until longer follow-up arrives. Candel Therapeutics funded the trial and plans to file for FDA approval late this year. Prostate cancer is the most common cancer in American men, and most cases are caught while still localized, which is exactly the setting this approach targets.

Key Takeaways

• Added to standard radiation, injected gene therapy lowered the risk of prostate cancer recurrence or death by 30%, and two-year biopsies were clean more often (80% versus 63%), without adding serious side effects.
• No survival benefit has emerged yet, and the therapy remains investigational; its maker plans an FDA application in late 2026.

References

1. DeWeese TL, Manzanera A, Sylvester J, et al. Aglatimagene besadenovec (CAN-2409) with radiotherapy for patients with localised prostate cancer: a phase 3, multicentre, randomised, double-blind, placebo-controlled trial. The Lancet Oncology. 2026;27(6):673–685. link