Cancer is primarily diagnosed by clinical presentation, radiology, biochemical tests and pathological analysis of tumor tissue, increasingly supported by molecular diagnostic tests. Molecular profiling of tumor tissue samples has emerged as a potential cancer classifying method. In order to overcome limitations of tissue acquisition the use of blood-based liquid biopsies has been suggested. Several blood-based sources are currently being evaluated as liquid biopsies, including plasma DNA and circulating tumor cells. So far, implementation of liquid biopsies for early detection of cancer has been hampered by non-specificity of these sources to pinpoint the nature of the primary tumor. It has been reported that tumor-educated platelets (TEPs) may enable blood-based cancer diagnostics. Platelets are circulating anucleated cell fragments that originate from megakaryocytes in bone marrow, and are traditionally known for their role in hemostasis and initiation of wound healing. More recently, platelets have emerged as central players in the systemic and local responses to tumor growth. Confrontation of platelets with tumor cells via transfer of tumor-associated biomolecules ('education') is an emerging concept and results in the sequestration of such biomolecules. Moreover, external stimuli, such as activation of platelet surface receptors and lipopolysaccharide-mediated platelet activation induce specific splicing of pre-mRNAs in circulating platelets. Platelets may also undergo queue-specific splice events in response to signals released by cancer cells and the tumor microenvironment -such as stromal and immune cells-. The combination of specific splice events in response to external signals and the capacity of platelets to directly ingest (spliced) circulating mRNA can provide TEPs with a highly dynamic mRNA repertoire, with potential applicability to cancer diagnostics. Additionally, the value of other biomarkers that can be derived from a liquid biopsy will be tested in this study. In addition, recently a hallmark paper has shown that combinations of protein tumor markers and ctDNA analysis could discriminate persons with different types of cancer from healthy controls with on average 70% sensitivity (at 99% specificity). In the case of ovarium cancer the sensitivity was 98%. Obvious advantages of liquid biopsy compared to tissue biopsy is the easy accessibility of the material to be obtained and the fact that tumor derived material in blood may cover the cancer heterogeneity where a tissue biopsy is limited to the alterations in the tumor punctured. Therefore, this study investigates the clinical value of longitudinal assessment of liquid biopsy-derived information in diagnosis and monitoring of treatment response in patients suspected of ovarian cancer.