SAN FRANCISCO – For patients with prostate cancer who have unfavorable features and a detectable PSA following a radical prostatectomy, the standard of care is treatment with 6 months of a gonadotropin-releasing hormone (GnRH) agonist with salvage radiation therapy (SRT), as established by the GETUG-AFU 16 trial.
A new trial, dubbed FORMULA-509, explored whether outcomes could be improved by intensifying the drug treatment by adding 6 months of abiraterone acetate plus prednisone as well as apalutamide on top of the GnRH agonist alongside the salvage radiotherapy.
However, the combination did significantly improve PFS and MFS in a subset of men with PSA levels greater than 0.5 ng/mL.
“Although this primary analysis did not meet the prespecified threshold for statistical significance, it does strongly suggest that the addition of abiraterone acetate/prednisone/apalutamide to salvage radiotherapy plus 6 months of ADT [androgen deprivation therapy] may improve progression-free survival and metastasis-free survival,” said lead author Paul L. Nguyen, MD, of the Dana-Farber Cancer Institute in Boston, and professor of radiation oncology at Harvard Medical School.
“This may be particularly evident in the subgroup of patients with PSA greater that 0.5 ng/mL where a preplanned subgroup analysis by stratification factors observed a statistically significant benefit for both progression-free survival and metastasis-free survival,” he said. “Six months of intensified ADT with next generation anti-androgens may provide an attractive alternative to lengthening ADT for patients with rising PSA and unfavorable features after radical prostatectomy.”
The study results were presented at the ASCO Genitourinary Cancers Symposium.
Benefit in subset
The FORMULA-509 trial included 305 patients with PSA ≥ 0.1 ng/mL who had undergone a radical prostatectomy, and who had one or more unfavorable risk features (Gleason 8-10 disease, PSA > 0.5 ng/mL, pT3/T4, pN1 or radiographic N1, PSA doubling time < 10 months, negative margins, persistent PSA, gross local/regional disease).
“This was a pretty high-risk population,” Dr. Nguyen emphasized, as 35% had Gleason score of 9, about a third (31%) a PSA >0.5, and 29% were pathologic node positive.
All patients received salvage radiotherapy plus 6 months of GnRH agonist (bicalutamide 50 mg), and half were randomly assigned to also receive abiraterone acetate/prednisone 1,000 mg/5 mg + apalutamide 240 mg daily.
At a median follow-up of 34 months, the 3-year PFS rate was 74.9% in the AAP-apalutamide arm vs. 68.5% for the control group (hazard ratio [HR], 0.71; P = .06), and the 3-year MFS rate was 90.6% vs. 87.2%, respectively (HR, 0.57; P = .05).
In the subset of patients with a PSA greater than 0.5 ng/mL, the 3-year PFS and MFS rates were significantly higher with in the AAP-apalutamide group: the 3-year PFS rate was 67.2% vs. 46.8% (HR, 0.50; P = .03), and the 3-year MFS rate was 84.3% vs. 66.1% (HR, 0.32; P = .02).
Adverse events were consistent with the known safety profiles of the agents being studied, Dr. Nguyen noted. The most common toxicities for AAP-apalutamide vs. controls were hypertension (21.8% vs. 13.3%), maculopapular rash (11.5% vs. 0.6%), diarrhea (8.5% vs. 4.8%), and fatigue (7.9% vs. 6.1%).
Dr. Nguyen noted that even though “we’re not supposed to compare clinical trials,” the results of this study appeared to compare favorably with those of another trial, RADICALS-HD, which was presented at the 2022 European Society of Medical Oncology Congress. That study showed that in patients undergoing postoperative radiation therapy, 24 months of ADT was superior to 6 months of ADT in improving both time to salvage ADT and MFS.
However, Dr. Nguyen emphasized that it would have to be formally tested, to see if “FORMULA-509 is performing in the ballpark of what 24 months of ADT would do.
“And I think that compared to 6 months of ADT, we can say it is certainly performing in the ballpark,” he said. “So, for patients with higher risk features, intensifying 6 months of ADT, I think, may be an appealing alternative to lengthening the ADT duration to 24 months.”
He added that this concept would be formally tested in the upcoming PROSTATE IQ study.
