In a European retrospective study (PORTAL) reported in The Lancet Oncology, Soeterik et al developed a nomogram for predicting androgen-deprivation therapy (ADT)–free survival with metastasis-directed stereotactic body radiotherapy (SBRT) in patients with prostate-specific membrane antigen (PSMA) positron-emission tomography (PET)-staged oligorecurrent prostate cancer.
Study Details
The study included patients from sites in Austria, Italy, Latvia, the Netherlands, Poland, and Portugal, including 586 in a development cohort and 131 in a validation cohort. Patients had received curative-intent local therapy and developed metachronous oligorecurrent, hormone-sensitive disease (≤ 5 PSMA PET-detected pelvic nodal or distant metastases or both). Between July 2014 and December 2023, patients received SBRT to all lesions, with no adjuvant systemic therapy being given. Development of the nomogram included evaluation of 10 clinical predictors in a multivariable Cox model; the primary outcome measure was proportion of patients remaining ADT-free at 1 year of follow-up.
Key Findings
In the development cohort, 52% of patients had pelvic nodal metastases and 48% had distant metastases. In the validation cohort, 44% had pelvic nodal metastases and 56% had distant metastases. Median follow-up was 37 months in the development cohort and 43 months in the validation cohort.
ADT-free survival at 1 year was 84.3% (95% confidence interval [CI] = 81.4%–87.3%) in the development cohort and 92.8% (95% CI = 88.4%–97.4%) in the validation cohort. Independent predictors of shorter time to ADT initiation were higher premetastasis-directed therapy prostate-specific antigen (PSA) level (hazard ratio [HR] = 1.05, 95% CI = 1.03–1.08), shorter PSA doubling time (HR = 0.97, 95% CI = 0.95–0.98), presence of three to five metastatic lesions (HR = 1.74, 95% CI = 1.33–2.28), and presence of distant metastases (HR = 1.45, 95% CI = 1.18–1.78).
The C-index values for the final nomogram model were 0.66 (95% CI = 0.65–0.68) in the development cohort and 0.65 (95% CI = 0.55–0.75) in the external validation cohort, indicating “modest” individual patient-level discrimination. However, the model provided significant discrimination of patients into three prognostic groups—low-risk, intermediate-risk, and high-risk (P <.0001).
The investigators concluded: “This nomogram predicts ADT-free survival after [metastasis-directed therapy] in oligorecurrent prostate cancer. While individual-level discrimination was modest, risk-group stratification showed meaningful separation, supporting its potential use in treatment selection.”
Timo F. W. Soeterik, PhD, of the Department of Radiation Oncology, University Medical Centre Utrecht, the Netherlands, is the corresponding author for The Lancet Oncology article.
DISCLOSURE: The investigators reported that there was no external funding for the study. For full disclosures of the study authors, visit thelancet.com.
