This research focuses on leveraging quantitative modeling to support dose selection in oncology drug development, presenting development of an exposure-tumour growth inhibition (E-TGI) model to investigate the relationship between brigimadlin exposure and tumour shrinkage using data from a phase I clinical trial. The aim was to support the selection of the recommended phase II dose (RP2D) for brigimadlin, a potent MDM2-p53 antagonist.