Abstract

Valeria Chiofalo¹, Giuseppe Carlo Iorio¹, Ilaria Bonavero¹, Ramona Parise¹, Roberta Carlevato¹, Sara Bartoncini¹, Veronica Richetto², Francesco Ceci³, Serena Grimaldi³, Sara Dall'Armellina³, Désirée Deandreis³, Beatrice Lillaz⁴, Marco Oderda⁴, Paolo Gontero⁴, Alessia Guarneri¹, Umberto Ricardi¹

¹University of Turin, Department of Oncology, Turin, Italy; ²University of Turin, Department of Medical Physics, Turin, Italy; ³University of Turin, Department of Medical Sciences, Nuclear Medicine, Turin, Italy; ⁴University of Turin, Department of Surgical Sciences, Urology, Turin, Italy

to evaluate the impact of PSMA-PET in the management of recurrent prostate cancer patients following radical prostatectomy (RP), with a main focus on RT.

we retrospectively analyzed data of patients experiencing biochemical recurrence (BCR) post-RP and staged at our Center with PSMA-PET prior to any treatment. Primary endpoints were: biochemical progression-free survival (bPFS) rate after any radiotherapy treatment guided by PSMA-PET (regardless of its result); and bPFS rate following any treatment. BCR was defined as PSA ³0.2 ng/ml. Secondary endpoints included: change in the treatment plan, defined as SRT abort or the addition of metastasis-directed therapy (MDT) to SRT, and rate of SRT abort. In patients treated exclusively with SBRT, as MDT, ADT-free survival was evaluated. Patterns of failure in patients receiving prostate-bed SRT following a negative PSMA-PET were also evaluated.

95 patients with BCR following RP (pN0-pNx) staged between November 2016 and March 2019 with PSMA-PET were included in the present analysis. The median follow-up time (PSMA to the last follow-up) was 36 months (range 11-50). The median PSA at PSMA was 0.5 ng/ml (range 0.13-8.9). PSMA was positive in 26 patients (27.3%), with 31 lesions detected as shown in Table 1. The SRT abort rate was 57.6% (15 patients), as only 9 patients underwent prostate-bed SRT guided by local PSMA uptake. A change in management was observed for 17 patients (65.3%). ADT only was administred in 4 patients (15.3%). One patient underwent SBRT+ADT and 2 patients received SRT+SBRT+ADT.  Exclusive MDT approaches included salvage pelvic lymph node dissection (s-PLND) for 3 patients (11.5%) and SBRT for 7 patients (26.9%).
Fifteen out of the 26 positive patients (57.6%) treated with PSMA-guidance experienced a recurrence, with a 9 months median interval from the end of any treatment (range 1-32). Among the 7 patients treated with SBRT-only 6 recurred with a median bPFS of 15 months (range 3-30). The median interval to ADT initiation in the SBRT-only group was 8 months (ADT-free survival).

PSMA following RP was negative in 69 patients, of whom 87% (60) received SRT (with ADT in 3/60). Among the remaining PSMA-negative patients, 7 were observed and 2 received ADT-only. After SRT 13 patients (21.6%) experienced a recurrence, with a median time of 6 months (range 1-28). Sites of recurrence following SRT in PSMA negative patients are shown in Table 1. Overall, a statistically significant difference (p<0.001) in terms of bPFS (Fig. 1) was recorded between PSMA negative patients treated with SRT (± ADT; n=57 as 3 patients were lost in follow-up) and PSMA positive patients that received targeted treatments (n=24, as 2 patients were lost in follow-up).

a high proportion of PSMA-positive patients had an actually delivered RT plan different from the intended SRT plan. PSMA-PET negativity at first BCR following RP strongly relates to better prognosis compared with the cluster of PSMA-positive patients.