For example, in FISH and quantitative PCR implementation, researchers evaluate the TMPRSS2-ERG fusion, AR gain, and PTEN loss in CTCs, primary tumor, and metastatic site of prostate cancer patients43; the fusion event of TMPRSS2-ERG in CTCs is also used as a biomarker for sensitivity of abiraterone acetate treatment in castration-resistant prostate cancer patients.44 Here, AR is linked to prostate cancer.