Despite significant improvements in the treatment and outcomes of early-stage breast cancer, the quest continues to find biological and molecular markers that would enable earlier diagnosis or better prediction of treatment efficacy and toxicity. Metabolomics—the latest and one of the most exciting of the ‘omic’ sciences—has shown early promise as a non-invasive diagnostic aid in ovarian cancer, and may allow the detection of subtle metabolic changes that could have diagnostic, prognostic or predictive value in breast cancer. Routine monitoring of circulating tumour cells (CTCs) has also been advocated as a novel means of detecting breast cancer progression earlier, and identifying alterations in tumour cells that might signal the need for therapy changes. Ongoing studies should help to answer important questions relating to the use of metabolomics and CTC evaluation as new strategies to monitor cancer progression and identify markers of chemotherapy activity and toxicity.