CST6 and breast cancer: To cite some examples, Chimonidou et al. detected promoter hypermethylation of two metastasis suppressor genes (MSG) (cystatin-M-precursor (CST6) and breast cancer metastasis suppressor 1 (BRMS1)) and one tumor suppressor gene (TSG) (SRY-box transcription factor 17 (SOX17)) in CTCs isolated from peripheral blood of breast cancer patients.