Ovarian cancer is the most deadly gynaecological malignancy and is characterised by initial response to first line therapy followed by relapse in more than 50% of cases . Unlike a number of other cancers, survival rates for ovarian cancer have not improved significantly over the last 25 years  and the first line treatment strategy for ovarian cancer has not changed significantly over this time period. One of the largest barriers to the development of new treatments is that early testing platforms do not accurately replicate the in vivo situation resulting in promising compounds failing at animal or human trials. Multicellular tumour spheroids (MCTS) are an in vitro biological model which closely replicates many aspects of the solid tumour and are predicted to bridge the gap between in vitro and in vivo drug testing . We have established this model in our lab using the ovarian cancer cell line: OV90, in order to test the efficacy of a small molecule inhibitor of CDK4/6. This compound inhibits cancer progression by interrupting the G1-S phase transition in the cell cycle and has exhibited activity against ovarian cancer in monolayer settings. In addition to cell death measurements, we have developed a MALDI mass spectrometry imaging (MSI) workflow for analysis of MCTS. This platform can deliver spatially resolved information about drug penetration, accumulation and metabolism in this biologically relevant model structure providing a window into the solid tumour and how it responds to treatment. The application of MALDI MSI analysis to the MCTS model holds great potential as a drug testing platform and we aim to use this model to test other novel anti cancer compounds into the future. Additionally, establishing MCTS from primary samples can further improve the biological relevance of the model and holds potential for personalised evaluation of drug efficacy.