Here we have shown that the key drivers of higher [1-13C]lactate labelling in the more aggressive subtype of intermediate-risk PCa are the combined tumour epithelial LDH (combined LDHA and LDHB), and the associated increase in tumour epithelium-to-stroma MCT4 expression, with both markers demonstrating a much stronger relationship with lactate SNR compared to epithelial MCT1 and epithelial or stromal MCT4 alone. The gene discussed is SLC16A3; the disease is neoplasm.