The search for ways to identify cancer stem cells is a subset of the broader search for commonalities in cancer: any biochemical similarity in cancer cells that marks them as different from normal cells is a potential opening for a targeted therapy. Here is an example of the sort of investigations presently taking place: "Despite many years of intensive effort, there is surprisingly little consensus on the most suitable markers with which to locate and isolate stem cells from adult tissues. By comparison, the study of cancer stem cells is still in its infancy; so, unsurprisingly, there is great uncertainty as to the identity of these cells. ... This review assesses the utility of recognizing cancer stem cells by virtue of high expression of aldehyde dehydrogenases (ALDHs), probably significant determinants of cell survival through their ability to detoxify many potentially cytotoxic molecules, and contributing to drug resistance. Antibodies are available against the ALDH enzyme family, but the vast majority of studies have used cell sorting techniques to enrich for cells expressing these enzymes. ... For many human tumours, but notably breast cancer, cell selection based upon ALDH activity appears to be a useful marker for enriching for cells with tumour-initiating activity (presumed cancer stem cells)."