Ovarian cancer (OC) is one of the most lethal cancers in the world due to late-stage disease at diagnosis. Standard therapy consists of debulking surgery and chemotherapy. However, despite this aggressive treatment, recurrent disease almost invariably occurs resulting in a five-year survival rate of approximately 30%. Immunotherapy could be a way to increase survival in OC patients. However, a major barrier to a successful deployment of cancer immunotherapy for ovarian cancer patients is the immunosuppressive tumor microenvironment. Envisioned solution/research direction Tumor-related inflammation is one of the hallmarks of cancers in general. Innate immunity specifically is a common denominator that is involved in the pathogenesis of OC. To improve the patient's outcome and identify novel therapeutic targets, one needs a deeper understanding of the tumor-induced changes in the bone marrow myeloid progenitor cells. Furthermore, treatment of these cells by nanoparticles or other agents that induce a program of 'trained immunity' may be a novel way to re- educate myeloid cells and their bone marrow progenitors in OC patients. Hypothesis We hypothesize that by exposing myeloid cells or their progenitors to various agents that induce trained immunity (e.g. trained immunity-inducing agents: BCG, heat-killed Candida,), these immune cells will undergo functional reprogramming to induce a tumor-suppressive phenotype. In the future, this could be explored as a novel immunotherapy for tumors that are refractory to conventional treatment. Objective To characterize and phenotype the immune state of OC patients compared to controls without cancer with a focus on the hematopoietic organs and the immune cells originating from these organs. In addition, the effect of established trained immunity-inducing agents on these cells will be evaluated in vitro, potentially providing new therapies. This will be executed by assessing the transcriptional, epigenetic, and functional reprogramming of circulating monocytes and myeloid progenitor cells in OC and by assessing the in vitro effect of trained immunity inducers on the reprogramming of circulating monocytes and myeloid progenitor cells. Study design: investigator-initiated, multi-center explorative cross-sectional study at the Catharina hospital Eindhoven, Radboud University Medical Center and Eindhoven University of Technology.