Metabolomics is the worldwide assessment and confirmation of endogenous small-molecule biochemicals (metabolites) within a biologic system. It is one of the "omic" sciences in systems biology. The metabolism of cancer cells is dysregulated to meet the demands of uncontrolled proliferation. This rewiring of cellular metabolism produces distinct metabolic phenotypes that can be exploited for earlier cancer detection, patient selection techniques for clinical trials, and/or treatment response biomarkers. Metabolomics aims to use cancer’s metabolic signature to estimate disease risk, detect cancer earlier, diagnose particular disease subtypes, and track treatment outcomes. In principle, metabolomics could aid in the rational selection of targeted medicines to meet cancer’s metabolic requirements.