SLC16A3 and neoplasm: Importantly, the tumour epithelium-to-stroma MCT4 ratio showed a positive correlation with the lactate SNR (rs = 0.90, P = 0.002; Fig. 2b, Supplementary Table 3) that was stronger than the correlation between epithelial MCT4 and lactate SNR (rs = 0.36, P = 0.31), demonstrating the potentially important role of metabolic compartmentalisation within the tumour in the interpretation of HP 13C-MRI.