With increasing treatment options for metastatic prostate cancer(mPC), there is a growing attention to circulating tumor cells(CTC)and circulating tumor DNA(ctDNA)as minimally invasive biomarkers to facilitate precision medicine. CTC count and ctDNA abundance have been reported to be prognostic factors. In addition, on-treatment changes in these values might also be associated with the treatment response. Androgen receptor gene alterations, including ligand-binding domain mutations, copy number amplification, or structural rearrangements, are identified in most metastatic castration-resistant prostate cancer(mCRPC)and associated with treatment response to androgen receptor pathway inhibitors. Alterations in different DNA damage repair genes, including BRCA2, ATM, CDK12, or mismatch repair genes, are linked to favorable response to targeted therapies such as poly(adenosine diphosphate-ribose)polymerase(PARP)inhibitors or immune checkpoint inhibitors. Overactivation of the PI3K signaling pathway is mainly caused by PTEN loss, and several clinical trials are underway to assess the treatment effect of the targeted therapies such as Akt inhibitors. To disseminate treatment strategies using CTC and ctDNA in clinical practice, we will require prospective biomarker-driven clinical trials, development of novel targeted therapies, and exploration of other molecular characteristics such as epigenome.