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Combining stereotactic body radiation therapy (SBRT) with standard systemic therapy yielded significant increases in the rates of biochemical response and progression-free survival (PFS) in patients with oligometastatic castrate-resistant prostate cancer (CRPC), the phase II randomized ARTO trial showed.

In a cohort of 157 patients at 6 months after the start of treatment, biochemical response was detected in 92% of those who received SBRT with abiraterone acetate (Zytiga) and prednisone versus 68.3% of those treated with standard systemic therapy alone (OR 5.34, 95% CI 2.05-13.88, P=0.001), reported Giulio Francolini, MD, of Azienda Ospedaliero Universitaria Careggi in Florence, Italy, and colleagues.

Complete biochemical response was observed in 56% of patients in the experimental arm versus 23.2% of those in the control arm (OR 4.22, 95% CI 2.12-8.38, P<0.001), they noted in the .

After a median follow-up of 24.9 months, median PFS was not reached in the experimental arm versus 17 months in the control arm, translating to a significantly reduced risk of progression with SBRT (HR 0.35, 95% CI 0.21-0.57, P<0.001).

"Median follow-up was long enough to suggest that these results are reliable and deserve attention, especially considering their magnitude," Francolini and colleagues concluded. "Phase III trials are warranted to test survival endpoints in larger cohorts."

The addition of SBRT also led to significant benefits in biochemical PFS (HR 0.33, 95% CI 0.16-0.67, P=0.002) and radiologic PFS (HR 0.39, 95% CI 0.19-0.81, P=0.011).

Overall, 24 patients died (nine in the experimental arm and 15 in the control arm). Median overall survival (OS) was not reached in either treatment arm, but there was a nonsignificant OS trend in favor of the experimental arm (HR 0.65, 95% CI 0.28-1.49).

Regarding safety, grade 1 and 2 adverse events (AEs) occurred in 64% and 65.8% of patients in the experimental and control arms, respectively. Grade >2 AEs occurred in 10.6% and 15.8%.

Most toxicities, including blood test abnormalities, fatigue, hot flashes, and hyperglycemia, were mild and related to systemic treatment, the authors noted.

Osteoporosis/fractures, hematuria, and gastrointestinal disorders were AEs considered potentially related to SBRT, with osteoporosis or fracture reported in two patients in the experimental arm and five in the control arm, hematuria in four patients in each arm, and gastrointestinal disorders in two patients in the experimental arm and one in the control arm.

Cardiovascular disorders were reported in 13.3% and 17% of patients in the experimental and control arms, respectively.

Jessica Wong, MD, MEng, of the Fox Chase Cancer Center in Philadelphia, told 名媛直播 that while new systemic therapies such as abiraterone and prednisone, as well as radiation techniques such as SBRT, have been able to improve outcomes for men with oligometastatic prostate cancer, "these treatments have not been compared directly in trials and the ARTO trial is the first to evaluate the synergistic effect of SBRT and AAP [abiraterone and prednisone] in men with oligometastatic prostate cancer."

"This trial showed that adding SBRT to systemic therapy including AAP improved progression-free survival as compared to AAP alone, without increasing the rate of adverse events," noted Wong, who was not involved in the study. "This shows that SBRT is safe and effective for treating oligometastatic prostate cancer concurrently with new systemic therapy agents."

The was conducted at 16 Italian centers and enrolled 157 patients (median age 74 years) from January 2019 through September 2022. Patients had to have metastatic CRPC with three or fewer bone or nodal metastatic lesions.

They were randomly assigned 1:1 to receive standard systemic treatment with abiraterone/prednisone, or standard treatment plus SBRT to all sites of metastatic disease. Patients were followed every 3 months with prostate-specific antigen (PSA) and complete hematologic blood tests.

The biochemical response rate (defined as the percentage of patients with a PSA decrease ≥50% compared with baseline at 6 months after start of systemic treatment) was the primary endpoint of the trial, while secondary endpoints included complete biochemical response rate (defined as the percentage of patients with a PSA ≤0.2 ng/mL at 6 months after start of systemic treatment) and PFS.

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