The Armstrong risk classification (ARC), which classifies CRPC patients into 3 groups according to 4 risk factors, including visceral metastases, bone scan progression, significant pain, and anemia (hemoglobin [Hb] level < 13 g/dL), is also a superior risk classification because it can be easily used in clinical practice without reducing the predictive abilities of nomograms and can predict not only survival but also post-chemotherapy prostate-specific antigen (PSA) declines and tumor responses [10]. Here, KLK3 is linked to anemia.