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In M1a prostate cancer (PC), disease has spread to non-regional lymph nodes and state-of-the-art treatment consist of systemic treatment with palliative androgen deprivation therapy (pADT) whether or not combined with second-line hormones or chemotherapy. However, using multimodality treatment (MMT) involving surgery, radiotherapy and ADT is gaining interest. We report on toxicity and early oncological results of MMT for M1a PC.

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.

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.

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.