In metastatic prostate cancer, the presence of the androgen receptor (AR) splice variant V7 in CTCs was previously demonstrated to be strongly associated with resistance to endocrine agents (Antonarakis et al., 2014), but not to chemotherapy (Antonarakis et al., 2015; Onstenk et al., 2015a; Scher et al., 2016). The gene discussed is AR; the disease is metastatic prostate carcinoma.