ASCO GU 2023: Development and Validation of a Multi-Institutional Nomogram of Outcomes for PSMA-PET–based Salvage Radiotherapy in Recurrent Prostate Cancer

( On the first day of the American Society for Clinical Oncology (ASCO) Genitourinary Cancer Symposium 2023 focussing on prostate cancer, Dr. Constantinos Zamboglou presented in Poster Session A the development and validation of a nomogram for patients undergoing salvage radiotherapy for biochemically-recurrent prostate cancer using PSMA-PET imaging.

There have been numerous studies, including prospective registration data, demonstrating the effect of molecular imaging using PSMA-based PET/CT on patient management after biochemical recurrence (BCR) following radical prostatectomy. However, there are a lack of data to guide patient management. Thus, these authors aimed to develop and to validate a multi-institutional nomogram of outcomes for PSMA-PET based salvage radiotherapy (sRT) following radical prostatectomy (RP) for patients with recurrent or persistent prostate cancer (PCa).

To do so, they obtained data regarding patients with a detectable post-RP prostate-specific antigen (PSA) treated with sRT with or without concurrent androgen-deprivation therapy (ADT) were obtained from 11 academic institutions from 5 countries. All patients had a PSMA-PET scan prior sRT and patients with distant metastases on PET were excluded from this analysis. The freedom from biochemical failure (FFBF) rate was estimated, and a predictive nomogram was generated and validated. Biochemical relapse (BR) was defined as PSA nadir +0.2 ng/ml after sRT.

They included a total of 1029 patients, of whom 821 contributed to the training set and 208 contributed to the external validation set. The median follow-up was 33 months. On PSMA-PET, 427 (42%) and 313 (30%) patients had local and nodal recurrences, respectively. Elective pelvic lymphatic nodal radiation was given in 368 (36%) patients. All patients received sRT to the prostatic fossa with doses of <66 Gy, 66-70 Gy and >70 Gy in 103 (10%), 551 (54%) and 375 (36%) patients, respectively. Androgen deprivation therapy (ADT) was given in 325 (32%) patients.

Using a multivariable Cox regression analysis, pre-SRT PSA, ISUP grade, pT stage, surgical margins, ADT use, sRT dose and nodal recurrence on PSMA PET were associated with FFBF. A nomogram based on these characteristics had a concordance index of 0.7 for FFBF in external validation.

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Thus, these authors have derived and validated a contemporary nomogram which can estimate individual patient outcomes after PSMA-PET guided sRT. They further identified positive lymph nodes on PSMA-PET as a risk factor for BR after sRT.

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Presented by: Constantinos Zamboglou, MD, Professor, Medical Center, University of Freiburg