Purpose First-line treatment of patients with recurrent, metastatic prostate cancer involves hormone therapy with or without additional systemic therapies. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) allows the detection of oligometastatic disease that may be amenable to image-guided radiotherapy. The current study classifies the type and localization of metastases and the clinical outcome of PSMA-PET/CT-guided radiotherapy to selected metastases. Materials and methods Between 2011 and 2019, 86 patients with recurrent, oligometastatic prostate carcinoma were identified by PSMA-PET/CT and were treated with image-guided radiotherapy of their metastases. Sites of relapse were characterized, and the primary endpoint overall survival (OS), biochemical progression-free survival (bPFS), and androgen deprivation therapy (ADT)-free survival were tabulated. Results In total, 37% of the metastases were bone metastases, 48% were pelvic nodal metastases, and 15% were nodal metastases outside of the pelvis. After PSMA-guided radiotherapy, a biochemical response was detected in 83% of the cohort. A statistically significant decrease in the standard uptake value (SUV) was seen in irradiated metastases. After a median follow-up of 26 months, the 3-year OS and bPFS were 84% and 55%, respectively. The median time of ADT-free survival was 13.5 months. A better clinical outcome was observed for patients receiving concomitant ADT or more than 24 fractions of radiation. Conclusion PSMA-guided radiotherapy is a promising therapeutic approach with excellent infield control for men with oligorecurrent prostate carcinoma. However, prospective, randomized trials are necessary to determine if this approach confers a survival advantage.

3010 Background: Checkpoint inhibition using PD-1/PD-L1 inhibitors does not show clinically relevant activity in MSS/pMMR (Mismatch Repair Proficient) colorectal cancer. Previous work showed that inhibition of CCR5 (C-C chemokine receptor type 5) leads to a macrophage re-polarization towards M1 macrophages within the tumor microenvironment which directly affects immune cell infiltrates. The current phase I trial explores a combined modification of the innate immune system (by CCR 5 blockade) and the adaptive immune system (by PD-1 inhibition) in the treatment of MSS CRC. Methods: 20 patients with metastatic MSS/pMMR colorectal cancer with failure of fluoropyrimidines, oxaliplatin, irinotecan, VEGF antibodies and EGFR antibodies (in ras WT patients) received pembrolizumab 200 mg q21d and maraviroc 300 mg bid cont. for 8 cycles, followed by pembrolizumab monotherapy for a maximum of 24 additional cycles. Imaging was performed every nine weeks (RECIST and irRECIST criteria). Primary endpoint was the feasibility rate (rate of patients receiving the protocol treatment during the core treatment without special event: treatment-related Grade ≥ 3 immune-related abnormalities, treatment-related Grade ≥ 4 AEs or any toxicity-related premature withdrawal of treatment). Secondary endpoints included safety/toxicity, ORR, PFS and OS. Results: 20 patients were enrolled. The median number of applied cycles was 3.5 for pembrolizumab and 3.5 for maraviroc. Two patients completed the core treatment period with pembrolizumab and started maintenance treatment. The feasibility rate was 94.7% (90% CI 77.4 to 99.7%), with one patient experiencing a special event. Except this grade 4 event (hyperglycemia) no ≥ 3 treatment-related toxicities were observed. According to irRECIST criteria one patient showed a partial response and one a stable disease as best response, resulting in an irDCR of 10.5%. Median PFS according to irRECIST was 2 months (CI 95%, 2 to 3), median OS 9 months (CI 95%, 6 to 20). Conclusions: Therapy with pembrolizumab and maraviroc was feasible and showed a beneficial toxicity pattern. Clinical activity in MSS CRC patients was limited, however prolonged disease stabilizations were observed in single patients and overall survival was higher than expected in this heavily pretreated population. Clinical trial information: NCT03274804 .