MKI67 and ovarian serous adenocarcinoma: ATRA treatment significantly increased the number of positive cleaved caspase 3 cells (Fig. 6a, p = 0.0024, Wilcoxon rank test) and significantly reduced Ki67 positivity (Fig. 6b, p = 0.0034, Wilcoxon rank test) in the serous ovarian cancer explant tissues.