A roadmap for quantifying metabolism in patients with cancer

Advancements in in vivo stable isotope tracing have revolutionized our understanding of cancer metabolism, transitioning the field from static metabolomic snapshots to dynamic metabolic pathway activities. However, interpreting raw fractional enrichment data presents significant biological and analytical challenges. This review systematically examines the methodological landscape of in vivo tracing, addressing the interpretive gap created by clinical constraints, such as single-timepoint surgical sampling. We dissect how secondary circulating tracers and the inherent heterogeneity of the tumor microenvironment can confound metabolic signals. We highlight the critical transition to metabolic flux analysis as the requisite computational step to overcome these challenges and to identify targetable metabolic vulnerabilities in precision oncology.