SURVIVAL EFFECT OF PALLIATIVE RADIOTHERAPY IN PATIENTS WITH METASTATIC CASTRATION-RESISTANT PROSTATE CANCER DEVELOPING OLIGO-PROGRESSION UNDER ANTIANDROGEN TREATMENT

Objective: Androgen pathway inhibitors have a significant impact on the treatment of prostate cancer. The treatment approach is controversial in patients who develop oligo-pro-gression under anti-androgen therapy. This study aimed to in-vestigate the effects of metastasis-directed stereotactic body radiotherapy (SBRT) on survival in the first-line setting of patients with metastatic castration-resistant prostate cancer who contin-ued the antiandrogen therapy after oligo-progression. Materials and Methods: Fifty-seven metastatic castration-re-sistant (serum testosterone <50 ng/dl) prostate cancer patients treated with abiraterone or enzalutamide in the first-line setting were analysed retrospectively. Thirty-nine of the patients with the oligo-progressive disease, which was defined as <= 3 lesions on imaging, received SBRT by continuing the same antiandro-gen therapy. Results: The median age was 70 (range 40-85). In the castra-tion-sensitive setting, 27 (47.4%) patients received docetaxel. The oligo-progressive metastatic sites were as follows: bone in 21 (52.3%), lymph node in 6 (15.3%) and visceral metastasis in 12 (30.9%) patients. Abiraterone and enzalutamide were preferred in 47.4% and 52.6% of patients, respectively. The 12-month pro-gression-free survival (PFS) was 79.0% and 88.9% in patients who received or did not receive SBRT (p<0.001). SBRT-related grade 1-2 toxicity was observed in 35 (61.4%) patients. SBRT was also an independent risk factor for PFS (p=0.007, HR:15.7; 95% CI 2.05-118.7). The presence of visceral metastases, isolated bone metastases, the choice of anti-androgen therapy, and Eastern Cooperative Oncology Group Scale Performance Status (ECOG PS) were not significantly associated with PFS. SBRT had no im-pact on overall survival. Conclusion: Patients treated with metastasis-directed SBRT without changing treatment in the oligo-progression setting had worse survival outcomes. Thus, metastasis-directed SBRT with continuation of the same antiandrogen therapy should be prior-itised only in selected cases.