3-year freedom from progression following ⁶⁸GaPSMA PET CT triaged management in men with biochemical recurrence post radical prostatectomy. Results of a prospective multi-center trial.

Abstract

Background: ⁶⁸Ga PSMA PET CT (PSMA) is increasingly used in men with biochemical recurrence (BCR) post radical prostatectomy (RP), but its longer term prognostic / predictive potential in these men is unknown. The aim of this study was to evaluate the predictive value of PSMA PET for 3 year freedom from progression (FFP) in men with BCR post RP undergoing salvage radiotherapy (sRT). Methods: This prospective multi-center study enrolled 260 men between 2015 and 2017. Eligible patients were referred for PSMA with rising PSA following RP. Management following PSMA was recorded but not mandated. PSMA protocols were standardised across sites and reported prospectively. Clinical, pathological and surgical information, sRT, timing and duration of androgen deprivation (ADT), 3 year PSA results and clinical events were documented. FFP was defined as a PSA rise ≤ 0.2ng/mL above nadir post sRT, with no additional treatment. Results: The median PSA was 0.26ng/mL (IQR 0.15 - 0.59) and follow-up 38 months (IQR 31-43). PSMA was negative in 34.6% (90/260), confined to prostate fossa 21.5% (56/260), pelvic nodes 26.2% (68/260), and distant disease 17.7% (46/260). 71.5% (186/260) received sRT, 38.2% (71/186) to the fossa only, 49.4% (92/186) fossa + pelvic nodes and 12.4% (23/186) nodes alone/SBRT. PSMA was highly predictive of FFP at 3 years following sRT. Overall, FFP was achieved in 64.5% (120/186) of those who received sRT, 81% (81/100) with negative/fossa confined vs. 45% (39/86) for extra fossa disease (p<0.0001). On logistic regression PSMA was more independently predictive of FFP than established clinical predictors, including PSA, T-stage, surgical margin status or Gleason score (P < 0.002). 32% of men with a negative PSMA PET did not receive treatment. Of these, 66% (19/29) progressed, with a mean rise in PSA of 1.59ng/mL over the 3 years. Conclusion: PSMA PET result is highly predictive of FFP at 3 years in men undergoing sRT for BCR following RP. In particular, men with negative PSMA PET or disease identified as still confined to the prostate fossa demonstrate high FFP, despite receiving less extensive radiotherapy and lower rates of additional ADT than those with extra fossa disease.