WASHINGTON -- Combining short-term androgen deprivation therapy (ADT) with high-dose radiotherapy improves disease-free survival in men with intermediate-risk prostate cancer compared with high-dose radiotherapy alone, according to results of the phase 3 GETUG 14 trial.

The 5-year disease-free survival rate was 84% in patients who received short-term ADT plus radiotherapy compared with 76% in those who received radiotherapy alone.

In addition, short-term ADT with high-dose radiotherapy didn't increase genitourinary or gastrointestinal toxicities, said Nicolas Demogeot, MD, with the Cancer Institute of Lorraine, Vandœuvre-lès-Nancy, France, who presented the results at the American Society for Radiation Oncology (ASTRO) 2024 Annual Meeting.

Adding short-term ADT to standard-dose radiotherapy has been shown to improve all clinical outcomes, Demogeot noted, but few trials have tested it with high-dose radiotherapy. GETUG 14 was designed to do just that.

The multicenter, randomized phase 3 trial enrolled 376 patients with intermediate- or high-risk localized prostate cancer who had PSA levels under 30 ng/mL and no clinical involvement of the seminal vesicles.

Patients were randomly allocated to high-dose radiotherapy (80 Gy) alone or high-dose radiotherapy plus monthly triptorelin and daily flutamide for a total duration of 4 months, starting 2 months prior to radiotherapy.

Disease-free survival was the primary endpoint. Secondary endpoints were overall survival, biochemical failure, metastasis failure, toxicity, and quality of life.

The modified intention-to-treat cohort included 191 patients in the radiotherapy-only group and 179 in the short-term ADT plus radiotherapy group. The two groups were well balanced. In both, patients ranged in age from 64 to 73 years; about two thirds had intermediate-risk disease; 70% received three-dimensional conformal radiotherapy, and 30% received intensity-modulated radiotherapy.

Overall, adding short-term ADT to high-dose radiotherapy was associated with a 36% relative improvement in 5-year disease-free survival (84% vs 76% with radiotherapy alone, hazard ratio [HR], 0.64; P = .02).

In subgroup analyses, intermediate-risk patients who received short-term ADT with high-dose radiotherapy demonstrated a significant improvement in disease-free survival (87% vs 74% with radiotherapy alone; HR, 0.55; P = .02). However, there was no significant disease-free survival benefit with short-term ADT with high-dose radiotherapy in high-risk patients (79% vs 75%; HR, 0.76; P = .40).

On multivariable analysis, short-term ADT with high-dose radiotherapy was associated with significant disease-free survival benefits (HR, 0.66; P = .038).

Patients who received short-term ADT with high-dose radiotherapy were significantly less likely to experience biochemical failure (10% vs 21%; HR, 0.45; P = .001), but there was no significant difference in metastasis failure (HR, 0.5; P = .09) or overall survival (HR, 1.22; P = .54).

As for adverse events, the two groups did not demonstrate significant differences in the proportions of early or late grade 2 or higher gastrointestinal or genitourinary toxicities.

Patients in the short-term ADT with high-dose radiotherapy group did experience a greater frequency of early grade 2 or higher erectile dysfunction (31% vs 6%; P < .001), but not late grade 2 or higher erectile dysfunction (63% vs 61%; P = .89).

Limitations of the study include a low power to detect differences between intermediate- and high-risk patients and the short follow-up period.

The GETUG 14 trial "confirms that short-term ADT improves disease-free survival when combined with dose-escalated radiation therapy for intermediate-risk prostate cancer," Mark A. Hallman, MD, PhD, with Fox Chase Cancer Center, Philadelphia, who was not involved in the study, told Medscape Medical News. "However, there was not a similar benefit among the smaller subpopulation with high-risk disease."

Outside expert Amar Kishan, MD, radiation oncologist, UCLA Jonsson Comprehensive Cancer Center, agreed, adding that "it is also reassuring to see no increase in genitourinary or gastrointestinal toxicity and no longer-term impact on erectile dysfunction."