The impact of rising PSA during salvage radiotherapy post radical prostatectomy on relapse.

Abstract

365 Background: Salvage radiotherapy (RT) is an effective curative salvage of relapse after radical prostatectomy (RP). CAPRA S score predicts for relapse after salvage RT. The DADSPORT meta-analysis suggests those with low CAPRA S score do not benefit from benefit of androgen ablation (AA) to salvage RT. A rising PSA during salvage RT may be important in predicting which patients may benefit from treatment intensification such as addition of AA to salvage RT. Herein we report on outcomes of salvage RT without AA in relation to rising PSA during RT. Methods: 32 patients were treated with salvage RT alone without AA (either because of low risk or patient preference) for rising PSA rising post RP. All patients had a PSA prior to and at least twice during RT at least 3 weeks apart. Patients were treated with 66 Gy in 33# to prostate bed. Patients were followed for PSA q 6 months post RT. Those with a PSA rising to over 0.2 were considered to have relapsed. Actuarial outcomes for relapse were assessed with multivariate analysis including CAPRA S score (low, intermediate, and high), and by 6 year progression free survival estimate from MSKCC nomogram (dichotomized around the median). Results: Median and IQR of PSA at time of salvage RT were 0.24 (0.2-0.55). 19% of patients had rising PSA during RT. 19 patients (60%) also received 46 Gy in 23# to pelvic nodes in phase 1 of RT. 34% of patients had PSMA PET prior to RT (none showing involved nodes or metastases). CAPRA S scores were low (15%), intermediate (69%), and high (15%). Relapse rates did not differ by CAPRA S score, although numbers were small. Three-year freedom from relapse rates were 16% for those with rising, and 49% without rising PSA during RT respectively (p=0.006). Three-year freedom from relapse rates were 9% for those below the median MSKCC nomogram risk, and 68% for those above the median respectively (p<0.001). Only rising PSA during RT was significant on MVA. Three patients had a rising PSA and a negative PSMA prior to salvage RT: all three relapsed within 1 year of RT. Of eight patients who had a falling PSA during RT and a negative PSMA PET prior to salvage RT: only 1 relapsed within 3 years of salvage RT. Conclusions: A rising PSA during salvage RT without AA is prognostic for relapse, and may be particularly relevant in the PSMA PET era. This may be a factor to considered when deciding whether to intensify therapy during salvage RT, either by adding adjuvant ADT, and/or using a PSMA PET to guide dose escalation.