Outcomes after salvage radiotherapy (SRT) are affected by various tumor-specific variables in men who underwent radical prostatectomy for prostate cancer, but using SRT at lower prostate-specific antigen (PSA) levels may also improve outcomes, according to a new study.
“The prognostic significance of PSA level at SRT initiation is well established for freedom from subsequent biochemical recurrence [BcR] as a therapeutic end point,” wrote study authors including Thomas M. Pisansky, MD, of the Mayo Clinic in Rochester, Minnesota. “However, data regarding an association between pre-SRT PSA and distant metastases or cause-specific mortality are currently limited.”
The new trial included 1,106 patients who underwent SRT between 1987 and 2013, with a median follow-up of 8.9 years. The results were published in the Journal of Clinical Oncology.
A total of 600 patients (54%) experienced a BcR, and the 5- and 10-year cumulative incidences of BcR were 49.9% and 64.3%, respectively. A multivariate analysis found that increasing tumor stage, Gleason score, and pre-SRT PSA levels were significantly associated with the risk of BcR. Each pre-SRT doubling of PSA had a hazard ratio (HR) for BcR of 1.30 (95% CI, 1.21–1.39; P < .001). An SRT dose above 68 Gy was also associated with lower risk of BcR.
A total of 208 patients developed distant metastases over the course of the follow-up period; the 5- and 10-year incidences of distant metastases were 10.9% and 19.9%, respectively. Again, a doubling of pre-SRT PSA was associated with increased risk, with an HR of 1.32 (95% CI, 1.19–1.46; P < .001). Rising Gleason score and tumor stage were also associated with distant metastasis formation.
There were 280 deaths during the study period, with 110 deaths attributed to prostate cancer. The multivariate analysis found that pathologic T3b tumors, Gleason score of 7 or higher, and a higher pre-SRT PSA were all associated with cause-specific mortality. Each doubling of PSA had an HR for cause-specific mortality of 1.40 (95% CI, 1.21–1.63; P < .001).
The authors noted that the observational case series nature of the study represents its greatest limitation, which may introduce selection bias. Still, they wrote that “these findings argue against prolonged monitoring of detectable post-radical prostatectomy PSA levels that delay initiation of SRT and serve as an important component of shared decision making between patient and physician.”