There is a lack of early predictive measures of outcome for patients with intermediate-risk prostate cancer (PCa) treated with stereotactic body radiotherapy (SBRT). The aim of the present study was to explore 4-year prostate-specific antigen response rate (4yPSARR) as an early predictive measure.
Individual patient data from six institutions for patients with intermediate-risk PCa treated with SBRT between 2006 and 2016 with a 4-year (42-54 months) PSA available were analysed. Cumulative incidences of biochemical failure and metastasis were calculated using Nelson-Aalen estimates and overall survival was calculated using the Kaplan-Meier method. Biochemical failure-free survival was analysed according to 4yPSARR, with groups dichotomised based on PSA <0.4 ng/ml or ≥0.4 ng/ml and compared using the Log-rank test. A multivariable competing risk analysis was carried out to predict for biochemical failure and the development of metastases.
Six hundred and thirty-seven patients were included, including 424 (67%) with favourable and 213 (33%) with unfavourable intermediate-risk disease. The median follow-up was 6.2 years (interquartile range 4.9-7.9). The cumulative incidence of biochemical failure and metastasis was 7 and 0.6%, respectively; overall survival at 6 years was 97%. The cumulative incidence of biochemical failure at 6 years if 4yPSARR <0.4 ng/ml was 1.7% compared with 27% if 4yPSARR ≥0.4 ng/ml (P < 0.0001). On multivariable competing risk analysis, 4yPSARR was a statistically significant predictor of biochemical failure-free survival (subdistribution hazard ratio 15.3, 95% confidence interval 7.5-31.3, P < 0.001) and metastasis-free survival (subdistribution hazard ratio 31.2, 95% confidence interval 3.1-311.6, P = 0.003).
4yPSARR is an encouraging early predictor of outcome in patients with intermediate-risk PCa treated with SBRT. Validation in prospective trials is warranted.
Clinical oncology (Royal College of Radiologists (Great Britain)). 2021 Nov 23 [Epub ahead of print]
R M Glicksman, A U Kishan, A J Katz, C A Mantz, S P Collins, D B Fuller, M L Steinberg, D Shabsovich, L Zhang, A Loblaw
Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada., Department of Radiation Oncology, University of California, Los Angeles, California, USA., St. Francis Hospital, Roslyn, New York, USA., 21st Century Oncology, Fort Myers, Florida, USA., Department of Radiation Oncology, Georgetown University, Washington, DC, USA., Division of Genesis Healthcare Partners Inc, Cyberknife Centres of San Diego Inc, San Diego, California, USA., Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada., Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; Institute of Health Policy, Management and Evaluation, University of Toronto, Ontario, Canada. Electronic address: .