Background: Androgen receptor-targeted therapies (ART) such as Abiraterone and Enzalutamide have shifted the management paradigm of metastatic castrate-resistant prostate cancer (mCRPC). These treatments are well-tolerated with less toxicities compared to chemotherapy, therefore methods to delay chemotherapy are beneficial to patients. Patients eventually become resistant to ARTs, and some patients will progress in a limited number of sites. This study investigated the prevalence of oligoprogressive disease (OPD) amenable to Stereotactic-body radiotherapy (SBRT). OPD is defined as ≤3 metastatic lesions which are progressing or new whilst all other sites of disease are well-controlled by ART. Methods: Retrospective analysis of electronic patient records and imaging studies of 95 patients treated with ART for mCRPC between April 2015 – 2017 from a single centre was undertaken. Data was analysed at the time of first tumour progression on ART. Results: The median (IQR) age of patients was 78.8 (74.4-83.6) years. OPD was found in 27 (28%) patients, 18 (19%) had lesions suitable for SBRT (Table). Seventeen (63%) patients were treated with abiraterone, 10 (27%) patients with enzalutamide. Median (IQR) time from starting ART to OPD was 16.4 (8.6-19.9) months. Five (19%) patients had 3 sites of OPD, 8 (29%) patients had 2 sites of OPD and 14 (52%) patients had 1 site of OPD. Nineteen patients continued ART beyond OPD for ≥3months. OPD was diagnosed using CT scan (56%), whole body diffusion-weighted MRI (22%), choline PET/CT (19%) and bone scan (3%). Six (22%) patients were treated with radiotherapy for OPD, 3 as participants of the TRAP trial (NCT03644303). Median time to subsequent progression after OPD for the 3 patients treated off trial with radiotherapy was 20.5 months. The OPD lesions treated with radiotherapy included the prostate (2 patients, 30 Gy in 5 and 24 Gy in 4 fractions) and para-aortic lymph node (1 patient, 30 Gy in 5 fractions). Median time to subsequent progression after OPD for those who did not receive radiotherapy was 6.4 months. There was no significant difference between median overall survival between patients with OPD and those who progressed with > 3 lesions (7 vs 9.2 years, P= 0.54). Ten (66%) patients who progressed after initial OPD on continuation of ART progressed with further OPD (≤3 lesions including original OPD lesion). Conclusions: OPD is prevalent in patients on ART for mCRPC. The most frequent site of OPD was in bone and majority of patients had only 1 site of OPD at presentation. These results identify a cohort of patients who may benefit from SBRT to maximise ART treatment. Fourteen (14%) patients met entry criteria for TRAP trial which is currently testing the role of SBRT to sites of OPD in mCRPC.