Ovarian cancer stem cell markers: prognostic and therapeutic implications

Abstract

Cancer stem cells are rare chemotherapy resistant cells within a tumor which can serve to populate the bulk of a tumor with more differentiated daughter cells and potentially contribute to recurrent disease. Ovarian cancer is a disease for which at the time of initial treatment we can obtain complete clinical remission in the majority of patients. Unfortunately, most will relapse and succumb to their disease. This clinical course is in line with the cancer stem cell model. In the past 5 years a significant amount of work has been done to identify cells with characteristics of ovarian cancer stem cells. This review will focus specifically on the markers used to define human ovarian cancer stem cells, the prognostic implications of the expression of these cancer stem cell markers in patient's primary tumors, and the potential of these cancer stem cell markers to serve as therapeutic targets.

Figure 1. Proposed hierarchy of ovarian cancer stem cell differentiation based on the current literature

A rare common ovarian CSC, for which markers have yet to be defined can give rise to either an ALDH⁺CD133⁺ early progenitor or a CD44⁺CD117⁺ early progenitor. Each of which can subsequently divide into more differentiated progenitors. The potential for expression of CD24 and CD44 in both lineages is indicated by the colored bars. Rounded arrows indicate cells with self-renewal capacity which have the potential to serve as CSC. Small arrows indicate the unproven potential for 'de-differentiation'.