Glycolysis is often upregulated in tumour cells but it can be inhibited by 3-bromopyruvate. Birsoy and colleagues found that monocarboxylate transporter 1 (MCT1) is required for 3-bromopyruvate uptake. The expression of SLC16A1 (which encodes MCT1) mRNA is a determinant of tumour cell sensitivity to 3-bromopyruvate, and its forced expression in tumour cells rendered xenografts sensitive to 3-bromopyruvate, indicating that MCT1 could be a biomarker of sensitivity to this drug.