Angiogenesis has been shown to play a crucial role in prostate cancer (PCa) progression in several preclinical models, in the clinic, pro-angiogenic factors have been shown to correlate with, Gleason score, metastasis and prognosis in PCa. Plasma levels of VEGF were shown to be higher in patients with metastatic PCa than those with localized disease. The natural killer (NK) cells have been found to be non cytolytic, immunosuppressed in solid cancers. Our group and others demonstrated that tumor infiltrating NK cells in lung and colorectal cancer acquire a pro-angiogenic phenotype. These cells are similar to NK cell within the decidua (dNK), and functionally support angiogenesis in a TGFb and Stat3-dependent manner. A similar subset is present in the peripheral blood of oncology patients. We characterized systemic peripheral blood NK cells (pNK) from PCa patients and their interaction with endothelial cells and macrophages. NK cell subset distribution was investigated by multicolor flow cytometry (FC) for surface antigens on peripheral blood samples PCa patients. Conditioned media (CM) of three different PCa cell lines were used to polarize the healthy donors pNK cells. CM from FACS-sorted PCa pNKs were used for functional studies of angiogenesis, on human umbilical-vein endothelial cells (HUVEC), studies for macrophage recruitment (migration assay on Boyden chambers) and polarization. Molecular studies were performed by real time PCR (qPCR) on HUCECs and macrophages exposed to CM of pNKs. Protein arrays were performed to characterize the secretome on FACS-sorted pNKs. We found that PCa pNKs acquire a pro-angiogenic/decidual-like CD56brightCD9+CD49a+CXCR4+ phenotype. The same phenotype was observed from healthy donors pNK cells exposed to CMs of three different PCa cell lines. These results were confirmed also exposing heathy-donor derived NK cells to conditioned media of 3 different prostate cancer cell lines (PC-3, DU-145, LNCaP), together with increased production of CXCL8, Angiogenin, Angiopoietin1 and reduced production of TNFa, IFNg and GranzymeA. CMs from pNK cells support the formation on capillary-like structures on HUVEC, together with increased expression of VEGF, VEGR-2, CXCL8, ICAM-1 and VCAM-1. Although in male patients, PCa NK cells resemble decidual-like ones. Finding these cells polarized in PB suggests that they could be used as non-invasive marker of inflammation in prostate cancer. Secretome analysis revealed the ability of pNK cells release pro-angiogenic factors (CLXL8, MMP-1, MMP-9; uPAR) and cytokines/chemokines involved in macrophage recruitment (CCL1, CCL2, CCL5, CCL7,CCL13, CXCL1, CXCL11) and M2-like polarization (IL-10). CMs from pNK can recruiting THP-1 monocyte and polarize THP-1 macrophage towards CD206, Arginase1, CXCL8-expressing M2-like/TAM phenotype. Our results place PCa pNK cells interaction with endothelial cells and via macrophage polarization able in supporting angiogenesis in PCa patients. Citation Format: Adriana Albini, Denisa Baci, Matteo Gallazzi, Federico Dehò, Angelo Naselli, Andrea Guernieri, Lorenzo Mortara, Douglas M. Noonan, Antonino Bruno. NK cells from prostate cancer patients acquire a pro-angiogenic phenotype and polarize macrophages towards a M2-like/TAM subset [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr LT006.