Given the intertumor variability, the absence of a defined scoring system, and the need to minimize any source of bias related to the use of a specific cut off value, the possible clinical role of CD133 expression in ovarian cancer was examined by Cox proportional hazard model using the percentage of Cd133 positive tumor cells as a continuous value, and by Kaplan and Meier analysis. This evidence concerns the gene PROM1 and ovarian cancer.