Ovarian cancer is the most lethal gynaecological disease, with poor 5-year survival rates and limited treatment options for patients who develop resistant disease. The majority of ovarian malignancies, up to 70% of cases, are high-grade serous carcinomas that have a high chemosensitivity to first line platinum-based therapies. However, 75% of patients will become chemoresistant, following relapse. The underlying mechanism for developing resistance to chemotherapy in ovarian cancer is poorly understood. In this study we employed Data Independent Acquisition (DIA) in a high-grade serous ovarian cancer (HGSOC) cohort (n=52) on formalin-fixed paraffin embedded FFPE samples from Munich Technical University. This method determines all ions that are selected within a specific m/z range, which are fragmented and analysed in a second level of tandem mass spectrometry. Over 3000 unique proteins were identified in our patient samples. Using Mass Dynamics we identified proteins that were up-regulated in patients that relapsed earlier (<24 months) compared to patients that relapsed after 60 months. One of these proteins was S100A10, a small 11kDa protein that forms a heterodimer in the plasma membrane with annexin A2 and plays an important role in the plasminogen activator pathway. Higher S100A10 expression was significantly associated with reduced progression-free survival in our patient cohort. Using online databases we found that S100A10 expression was significantly associated with chemotherapy resistance and reduced overall survival. S100A10 protein expression was significantly increased following chemotherapy treatment. Functional studies demonstrated that S100A10 neutralizing antibodies or treatment with siRNA S100A10 significantly reduced the motility and invasion of OV90 and OVCAR5 ovarian cancer cell lines. In conclusion, S100A10 is a viable therapeutic target for HGSOC.