This clinical study is an open-label, multicenter, interventional, Phase 4 study to evaluate changes in genomic alterations for 73 PC driver genes during apalutamide treatment in patients with mCSPC. A total of 100 participants to be treated by apalutamide will be registered in this study. All participants will undergo blood collection for ctDNA, single-nucleotide polymorphisms (SNPs), and human-leukocyte antigen (HLA) typing at pre- and posttreatment of apalutamide.