Add-On Prostate Radiotherapy for De Novo Low-Volume mCSPC Improves Outcomes

Adding prostate radiotherapy (RT) to intensified systemic therapy improves outcomes in de novo metastatic castration-sensitive prostate cancer (mCSPC) with low metastatic burden, according to research presented at the ASCO Annual Meeting 2023. 

Patients with low-volume mCSPC who received RT in combination with standard of care (SOC) and abiraterone had a significant improvement in radiographic progression-free survival (rPFS). Patients who received RT plus SOC, with or without abiraterone, had significantly longer castration resistance-free survival. 

In addition, RT decreased the likelihood of serious genitourinary events regardless of metastatic burden, said study presenter Alberto Bossi, MD, of Gustave Roussy Cancer Institute in Villejuif, France. 

This analysis, from the phase 3 PEACE-1 trial (ClinicalTrials.gov Identifier: NCT01957436), included 1172 patients with mCSPC. They were randomly assigned to receive SOC alone (n=296), SOC with abiraterone (n=292), RT plus SOC (n=293), or RT plus SOC and abiraterone (n=291). SOC was androgen deprivation therapy (ADT) alone or in combination with docetaxel. 

Low-volume metastases (0 to 3 metastatic sites with or without lymph node metastases) were present in 252 of the 584 patients who received RT and 253 of the 588 patients who did not receive RT. 

In the low-volume population, the median rPFS was significantly longer in the RT-SOC-abiraterone arm than in the other 3 arms. The median rPFS was:

• 3.0 years in the SOC arm (reference)
• 2.6 years in the RT-SOC arm (hazard ratio [HR], 1.11; 99.9% CI, 0.67-1.84) 
• 4.4 years in the SOC-abiraterone arm (HR, 0.76; 99.9% CI, 0.45-1.28)
• 7.5 years in the RT-SOC-abiraterone arm (HR, 0.50; 99.9% CI, 0.28-0.88; global P <.0001). 

When compared with patients who received SOC alone, there was no significant improvement in rPFS for patients who received RT-SOC (HR, 1.08; 99.9% CI, 0.65-1.80; P =.61). However, when compared with patients who received SOC-abiraterone, there was a significant improvement in rPFS for those who received RT plus SOC-abiraterone (HR, 0.65; 99.9% CI, 0.36-1.19; P =.02). 

The 2 RT arms were pooled for the overall survival (OS) analysis, which showed that RT did not significantly improve OS in the low-volume population. The median OS was 7.5 years among patients who received RT plus SOC with or without abiraterone and 6.9 years for patients receiving SOC with or without abiraterone (HR, 0.98; 95% CI, 0.74-1.28; P =.86). 

On the other hand, patients in the low-volume population who received RT had significantly longer castration resistance-free survival. The median was 3.4 years in patients who received RT and 2.5 years in those who did not (HR, 0.74; 95% CI, 0.60-0.92; P =.007). 

In the overall study population, there were 58 serious genitourinary events in patients who received RT and 106 in patients who did not (P =.0001). In the low-volume population, there were 24 serious genitourinary events in patients who received RT and 52 events in patients who did not (P =.0006). 

“A triplet of ADT plus abiraterone and prostate radiotherapy should be considered a standard of care in men with de novo low-burden metastatic castration [sensitive] prostate cancer,” Dr Bossi said. “We are also convinced that radiotherapy may be considered in men with de novo high-burden metastatic castration [sensitive] prostate cancer.” 

PEACE-1 also establishes a role for RT in the prevention of serious genitourinary events, independent of metastatic burden, Dr Bossi added.

Disclosures: This research was supported by Ipsen, Janssen, Sanofi, and Unicancer. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

Reference

Bossi A, Foulon S, Maldonado X, et al. Prostate irradiation in men with de novo, low-volume, metastatic castration-sensitive prostate cancer (mCSPC): Results of PEACE-1, a phase 3 randomized trial with a 2×2 design. ASCO 2023. June 2-6, 2023. Abstract LBA5000.