236 - Intermittent Androgen Deprivation Therapy Plus Comprehensive Stereotactic Body Radiotherapy for Hormone Sensitive Oligometastatic Prostate Cancer: Mature Results of a Prospective Trial
Presenter(s)
P. Cheung1, C. L. Tseng1, H. T. Chung1, W. Chu2, D. Vesprini1, S. K. Liu1, A. Sahgal1, H. Soliman1, S. D. Myrehaug1, J. Detsky1, E. Szumacher1, P. Chung3, J. Helou4, U. Emmenegger5, V. Escueta1, A. Mamedov1, L. Zhang6, G. Morton1, and D. A. Loblaw1; 1Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada, 2Durham Regional Cancer Centre, University of Toronto, Oshawa, ON, Canada, 3Department of Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, 4Division of Radiation Oncology, Western University, London, ON, Canada, 5Divsion of Medical Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, ON, Canada, 6MacroStat Inc., Toronto, ON, Canada
Purpose/Objective(s): This prospective phase I/II study assessed the utility of SBRT to all tumor sites plus intermittent androgen deprivation therapy (ADT) in patients with hormone sensitive oligometastatic prostate cancer. Endpoints included incidence of SBRT induced late grade 3+ toxicities and clinical outcomes including cumulative incidences of restarting ADT, developing local failure, new metastases, castration resistant prostate cancer (CRPC), and overall survival (OS).
Materials/Methods: Synchronous and metachronous metastatic disease presentations were eligible if there were = 5 metastases, with = 3 metastases in any one organ system. Conventional scans (CT/bonescan +/- MRI) were used to stage patients at baseline, although novel PET imaging was optional. SBRT was delivered to all sites of disease, including the prostate if not previously treated. ADT was started prior to or immediately after SBRT and was continued for 1 year before moving to an intermittent approach. ADT was restarted for another year when the PSA reached = 10 ng/mL or earlier if clinically indicated (development of new metastases or rapidly rising PSA). If new metastases developed in an oligometastatic fashion, SBRT was delivered to the new lesions in conjunction with restarting ADT. Toxicity (CTCAE v4.0) and PSA measurements were collected every 4 months during follow-up. Conventional scans were performed at a minimum of once per year, but more frequent imaging was allowed at the discretion of the physician. Time zero was date of patient consent.
Results: 89 evaluable patients with 171 metastases were accrued with a median age of 74 years. Median follow-up time was 6.2 years. Median baseline PSA was 8.3 ng/mL (IQR 4.2 – 16.3). 39 (43.8%) patients had Gleason score of 8-10. 33 (37.1%) patients had synchronous presentation, and 14 (15.7%) patients had additional PET staging. One (1.1%) patient developed late grade 3 GU toxicity, 5 (5.6%) patients developed a SBRT induced bone fracture, and no grade 4/5 toxicities were observed. Median PSA nadir was 0.04 ng/mL after SBRT and 1 year of ADT. The 5-year rate of restarting ADT was 69.9%. 35 (39.3%) patients were alive and off ADT at last follow-up. 36 (40.4%) patients had subsequent rounds of SBRT at time of radiographic progression. The 5-year freedom from any failure (defined as biochemical or radiographic failure or restarting ADT) rate was 16.3%. The 5-year rates of developing local failure (at site of SBRT), new metastases, and CRPC were 9.0%, 56.1% and 22.8%, respectively. 5-year OS was 78.2%.
Conclusion: Combining SBRT with intermittent ADT for hormone sensitive oligometastatic prostate cancer was safe and efficacious. With > 6 years of median follow-up, overall survival was high, and a small number of patients may be “cured” after SBRT and 1 year of ADT. The incidence of developing CRPC was low, as compared to modern landmark systemic therapy trials using continuous ADT for metastatic prostate cancer. Potential factors which predict for oncologic outcomes will be presented.