OLI-P: Toxicity and efficacy of local ablative radiotherapy in PSMA-PET staged, oligometastatic prostate cancer—A phase II trial

115 Background: After curative primary therapy, a subset of patients with prostate cancer will have PSA-progression. Modern imaging methods may detect patients with oligometastastic disease at an early time point. Local ablative therapy has shown to improve time to progression compared to standard of care. PSMA-PET hybrid imaging is an emerging method, with a high accuracy and sensitivity to detect oligometastatic disease at low PSA-levels. Methods: At two German centers, patients with PSA progression after local curative treatment had PSMA-PET- hybrid imaging. Patients with up to five PSMA-PET positive metastases were offered to participate in the clinical trial. Further relevant exclusion criteria were ongoing androgen deprivation therapy (ADT), PSA >10 ng/ml or severe comorbidity. The patients had a local ablative radiotherapy (aRT) to all PSMA-PET positive metastases. The primary endpoint was toxicity within two years after aRT. Secondary endpoints included PSA-progression free survival (defined as PSA nadir +1 ng/ml or start of ADT) and therapy-free survival (i.e. time to start ADT). Results: Between 2014 and 2018, 72 patients were included; patients’ characteristics are shown in table. Nine patients were excluded as no aRT was performed. The median follow up for the remaining 63 patients was 34.2 months. Within two years, 67 % (42 of 63 pats) had no report of adverse events. Following events were recorded during follow up: rectal bleeding (Grade 1, n=1), stroke (1), urinary incontinence (grade 2: n=3) secondary malignoma (n=5, primary liver tumor (n=2), bladder cancer, acute leukemia and head and cancer). All adverse events were considered as “not related“ to aRT of the metastases. PSA progression occurred in 44 patients after a median of 14.4 months. After two years, PSA relapse free survival was 38.2 %. ADT was initiated in 36 patients after a median of 26 months; 54 % (n=34 of 63) did not start ADT within two years after aRT. Conclusions: Local ablative radiotherapy in selected patients with PSMA-PET staged oligometastatic prostate cancer is well tolerated and may improve midterm outcome and delay onset of systemic therapy. Clinical trial information: NCT02264379. [Table: see text]