Cancer cells evolve by acquiring new mutations, which they pass on to daughter cells. Cells with a common set of mutations, suggesting a shared evolutionary history, are called clones. Typically, a patient cancer sample contains a mix of clones. We spatially mapped the spread of the cancer in 5 patients with treatment-naive locally advanced prostate cancer using whole genome sequencing from 42 systematically sampled primary prostate cancer tissue and lymph node metastases. We analysed a total of >19,000 copy number corrected single nucleotide variants, which enabled us to decipher the evolutionary relationships between the cancer clones in each individual. Based on this phylogenetic reconstruction, we identified specific clones and their locations in the prostate gland that likely seeded the lymph node metastases. We also observed an association between phylogenetic branching and histological heterogeneity which if validated in a larger cohort will have implications for diagnosis and risk stratification. In addition to presenting these results, I will also provide an update on our current research which builds on this study.