Metastasis-directed Therapy in Prostate Cancer: Prognostic Significance of the ESTRO/EORTC Classification in Oligometastatic Bone Disease

• Published in: Clinical oncology (Royal College of Radiologists (Great Britain)) 2022-01, Vol.34 (1), p.63-69
• Main Authors: Nicholls, L., Chapman, E., Khoo, V., Suh, Y.-e., Tunariu, N., Wang, Y., van As, N.
• Format: Article
• Language: English
• Subjects: Bone metastases; Bone Neoplasms - therapy; Humans; Male; oligometastatic; Prognosis; Prospective Studies; prostate cancer; Prostatic Neoplasms - therapy; Radiosurgery; Retrospective Studies; stereotactic body radiotherapy
• ISSN: 0936-6555; 1433-2981
• DOI: 10.1016/j.clon.2021.10.004

Oligometastatic disease (OMD) represents a spectrum of clinical scenarios and various classification systems have been proposed. Bone-only OMD can occur in patients with advanced prostate cancer and validated decision-making tools are needed to assist patient selection for metastasis-directed therapy. The aim of the present study was to determine the prognostic utility of a classification system for OMD. A retrospective review was conducted of all patients with bone-only oligometastatic prostate cancer treated with stereotactic body radiotherapy (SBRT) since November 2011. SBRT was delivered using CyberKnife® and gantry-based linear accelerator platforms. All patients were classified into oligometastatic states based on the European Society for Radiotherapy and Oncology/European Organisation for Research and Treatment of Cancer (ESTRO/EORTC) classification system. Kaplan–Meier and Cox regression analyses were carried out to determine the prognostic utility of this classification system. In total, 105 patients with 145 osseous metastases were treated over 119 sessions. The median follow-up after SBRT was 23 months (interquartile range 10–39.8). Twelve patients had died after a median time of 31 months. The 3-year metastatic progression-free survival was 23% (95% confidence interval 13–32) and the 3-year overall survival was 88% (95% confidence interval 80–96). Patients in a metachronous oligometastatic state were 4.50 (95% confidence interval 1.19–17.10, P = 0.03) times more likely to experience metastatic progression compared with those with synchronous oligometastases, and 6.69 (95% confidence interval 1.05–42.50, P = 0.04) times more likely to experience any failure. Hazard ratio magnitudes increased for patients in a repeat oligometastatic state. The multivariate model for both metastatic progression-free survival and failure-free survival found prostate-specific antigen doubling time