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Objectives Patients and Methods Results Conclusions To prospectively compare systemic anti‐tumour immune responses induced by irreversible electroporation (IRE) and robot‐assisted radical prostatectomy (RARP) in patients with localised intermediate‐risk prostate cancer (PCa).Between February 2021 and June 2022, before and after treatment (at 5, 14 and 30 days) peripheral blood samples of 30 patients with localised PCa were prospectively collected. Patient inclusion criteria were: International Society of Urological Pathologists Grade 2–3, clinical cancer stage ≤T2c, prostate‐specific antigen level <20 ng/mL). Patients were treated with IRE (n = 20) or RARP (n = 10). Frequency and activation status of lymphocytic and myeloid immune cell subsets were determined using flow cytometry. PCa‐specific T‐cell responses to prostatic acid phosphatase (PSAP) and cancer testis antigen (New York oesophageal squamous cell carcinoma 1 [NY‐ESO‐1]) were determined by interferon‐γ enzyme‐linked immunospot assay (ELISpot). Repeated‐measures analysis of variance and two‐sided Student's t‐tests were used to compare immune responses over time and between treatment cohorts.Patient and tumour characteristics were similar between the cohorts except for age (median 68 years [IRE] and 62 years [RARP], P = 0.01). IRE induced depletion of systemic regulatory T cells (P = 0.0001) and a simultaneous increase in activated cytotoxic T‐lymphocyte antigen 4 (CTLA‐4)+ cluster of differentiation (CD)4+ (P < 0.001) and CD8+ (P = 0.032) T cells, consistent with reduction of systemic immune suppression allowing for effector T‐cell activation, peaking 14 days after IRE. Effects were positively correlated with tumour volume/ablation size. Accordingly, IRE induced expansion of PSAP and/or NY‐ESO‐1 specific T‐cell responses in four of the eight immune competent patients. Temporarily increased activated myeloid derived suppressor cell frequencies (P = 0.047) were consistent with transient immunosuppression after RARP.Irreversible electroporation induces a PCa‐specific systemic immune response in patients with localised PCa, aiding conversion of the tumour microenvironment into a more immune permissive state. Therapeutic efficacy might be further enhanced by combination with CTLA‐4 checkpoint inhibition, potentially opening up a new synergistic treatment paradigm for high‐risk localised or (oligo)metastatic disease. [ABSTRACT FROM AUTHOR]