ESTRO 2020 Abstract book

S680 ESTRO 2020

Material and Methods We conducted a retrospective database analysis in a tertiary referral centre and analysed the outcome of patients who were treated with MMT for M1a PC. Three different groups were analysed: upfront metastatic, recurrent or castration-refractory prostate cancer (CRPC). Patients with M1b or M1c disease were excluded. Patients were treated with super-extended lymph node (LN) dissection and/or (stereotactic body) radiation therapy (RT), whether or not combined with systemic treatment. Study time frame was 1-2018 until 9-2019. Results In total, 43 patients were eligible for the study. In 95% of the cases (n=43), M1a disease consisted of positive para- aortic (PALN). One patient had positive mediastinal/hilar LN and another patient had the combination of PA, inguinal and supraclavicular LN. In 29 patients (67%), N1 disease was present. Ten patients had upfront M1a PC, 29 recurred as M1a disease and 4 were CRPC. Thirty-six patients (84%) received concomitant ADT with a median duration of 24 months. In 14% (5/36) of those patients systemic treatment other than ADT was combined. As MDT, patients received surgery (21%), RT (26%) or both (53%). Further treatment specifics can be found in table 1. Three patients experienced late grade 3 toxicity. One patient experienced late grade 3 gastro-intestinal obstruction for which hospitalisation was needed and treatment was conservative. One patient developed an abscess in the iliopsoas muscle treated with a surgical evacuation. The third needed a surgical revision because of leakage of an urinary stoma. In all patients toxicity resolved completely over time.Two patients experienced grade 4 toxicity: one patient had a multi-organ problem, consisting of radio- enteritis based bowel obstruction, urosepsis, cardiac failure and radiocystitis with consequent renal dysfunction needing bilateral nephrostomies which will be needed lifelong. The other patient had a post-operative arterial bleeding with hypovolemic shock for which an urgent surgical re-intervention was needed. Postoperative, there was a transient right hemiplegia, which resolved completely. For a median follow-up of 26 months (IQR: 12-40), median clinical relapse free survival was 44 months (95% CI: 28-59) and mean cancer-specific survival was 104 months (95%CI 96-113) (median not reached, only 2 events). Oncological outcomes will be updated and presented at ESTRO 2020.

Conclusion MMT for M1a PC is feasible, with grade 3 and 4 toxicity occurring in a minority of patients. Although follow-up is short, first results on cancer-specific survival are promising. PO-1201 Oligorecurrent prostate cancer treated with metastasis-directed therapy: oncological outcomes G. Devos 1 , C. Berghen 2 , S. Joniau 1 , K. Poels 2 , K. Haustermans 2 , K. Rans 2 , G. De Meerleer 2 1 University Hospital Gasthuisberg, Urology, Leuven, Belgium ; 2 University Hospital Gasthuisberg, Radiation Oncology, Leuven, Belgium Purpose or Objective To evaluate the oncological results of treatment with metastasis-directed therapy (MDT) for patients presenting with oligorecurrent hormone-sensitive prostate cancer (HSPC). Material and Methods We retrospectively analysed the outcome of patients treated with MDT for oligorecurrent HSPC, defined as the recurrence of 1-5 pelvic nodal (N1) and/or metastatic lesions (M1a-c) following maximal treatment of the primary tumor. Between 01/2005 and 01/2019, 215 patients with 406 lesions were included in this analysis. Results Of the 215 patients, 87 patients (151 lesions) were treated with radiotherapy, of which 55 (82 lesions) were treated with stereotactic body radiation therapy (SBRT). 117 patients were treated with lymphadenectomy (LAD) for cN1 or cM1a disease OR metastasectomy for M1b/c disease (n=11). In case of pN1 disease after LAD, postoperative pelvic/retroperitoneal radiotherapy was administered together with 24 months of androgen-deprivation therapy (ADT). In case of SBRT to a metastatic lesion, 1 month of ADT was given as radiosensitizer. In total, 115 patients (53%) received ADT. After a median follow-up of 35 months (IQR 19-61 months), the median clinical relapse-free survival was 27 months (95% CI 23-32). The ADT-free survival was 65 months (95% CI 49-83). The median ADT-free survival for patients with only N1 disease was significantly longer than patients with the M1a-c disease: not reached vs. 65 months (95% CI 49- 83, p=0.02). The median castration-refractory prostate cancer (CRPC)-free survival and median cancer-specific survival (CSS) were not reached, with only 34 and 8 events respectively, resulting in crude CRPC-free survival of 80% at 5 years. Crude CSS was 95% at 5 years.