Over the years, PSA glycosylation changes have been analysed by mass spectrometry, and the level of α2,3-linked sialic acid was reported to be remarkably different in prostate cancer patients compared to a control group, stressing the importance of PSA sialylation in distinguishing cancer patients from healthy men (Figure 1B) [14,16,70]. Here, KLK3 is linked to prostate cancer.