In this review, we summarize the current knowledge on blood-based liquid biopsy analyses in prostate cancer focusing on disease- and therapy-related changes in PSA and related molecules, immune cells and immune- and inflammation-related secreted factors, circulating tumour cells (CTCs) and tumour-derived cell-free circulating nucleic acids as well as extracellular vesicles (EVs) and their micro-RNA (miRNA) content (Figure 1 and Table 1). The gene discussed is KLK3; the disease is Familial prostate cancer.