Interim PSA: Predicting for Biochemical Failure during Salvage Radiotherapy Following Prostatectomy

Abstract

It is challenging to identify patients at higher risk of biochemical failure following salvage radiotherapy after having a radical prostatectomy. This work aims to determine if an interim PSA during radiotherapy would predict two year biochemical failure for patients who have salvage radiotherapy for a rising PSA following a radical prostatectomy for prostate cancer. A total of 185 patients in one center having salvage radiotherapy following a radical prostatectomy to a dose of 68Gy without androgen deprivation therapy between the years of 2010 and 2016 had their PSA recorded on the first day of radiotherapy, and again after completing the 25th fraction of 34 total fractions. Biochemical failure after radiotherapy was defined as a PSA value ≥0.2ng/mL within two years following radiotherapy. Univariate and multivariate Cox regression models were used for statistical analysis using statistical software. Factors investigated in univariate analysis other than a drop in PSA during radiotherapy included age, a Gleason score above 7, surgical margins status, the presence of extracapsular extension, PSA doubling time prior to radiotherapy, PSA at the time of radiotherapy, the presence of a detectable post-operative PSA immediately after surgery, whether or not a pelvic lymph node dissection was performed and whether or not there was seminal vesicle invasion. Factors with a p value <0.2 in univariate analysis were then used in a multivariate analysis. The two year freedom from biochemical failure was 60% (95% CI: 53% to 67%). Table 1 shows that on multivariate analysis, a drop in PSA during radiotherapy (p=0.003) and a positive surgical margin (p<0.0001) were significant factors for freedom from subsequent biochemical failure, while seminal vesicle invasion was associated with biochemical failure at two years (p=0.007). A PSA rise during salvage radiotherapy is predictive of biochemical failure at two years (HR 2.05). Factors such as seminal vesicle invasion and a negative surgical margin also predict for poor responders to salvage radiotherapy. If this is confirmed in further studies, then it may allow salvage radiotherapy to be abandoned at 50Gy into the treatment course, thereby potentially averting further futile radiotherapy and the risks of higher dose salvage treatment.Abstract 2619; Table 1Prognostic factors for biochemical failure at two years on multivariate analysis. *[Reference value]PSA During RadiotherapySurgical MarginsSeminal Vesicle InvasionGleason scoreSame or riseFallNegativePositiveYesNo>7≤7HR(95% Cl)2.050 (1.273-3.299)1*2.437 (1.493-3.978)1*2.044 (1.218-3.431)1*1.247 (0.731-2.127)1*P Value0.003<0.0010.0070.418 Open table in a new tab