To test this, we used pre-validated sandwich ELISA assays22 to monitor ST6GAL1 protein levels in a cohort of 300 serum samples, including 40 men given a ‘no cancer diagnosis’, 100 men with low grade prostate cancer (Gleason grade 6–7), 100 men with high grade prostate cancer (Gleason grade 8–9), and 60 men with metastatic CRPC (Supplementary Table S1). The gene discussed is ST6GAL1; the disease is cancer.