ESR1 and ovarian cancer: Among these, miR200b might be the best candidate due to the following reasons: (i) it showed a well-detectable expression level in ERα-expressing cells; (ii) its intracellular and cell-free expression level responded well to E2; (iii) its transcription is supposed to be regulated by ERα; (iv) its expression was well detectable in the plasma samples of patients with ovarian tumors and it proved to be an applicable biomarker in ovarian cancer in our previous studies [24].