However, it remains unknown which parameter of cell-free DNA is correlated with the progression and prognosis of metastatic castration-resistant prostate cancer.<h4>Case presentation</h4>A 75-year-old man with newly diagnosed prostate cancer (serum prostate-specific antigen 4891 ng/mL, Gleason score 4 + 5 = 9, cT3bN1M1) was referred to our department. The gene discussed is KLK3; the disease is Familial prostate cancer.