In an effort to improve our understanding and treatment of cancer, a new model of tumorigenesis is being developed - the cancer stem cell model. Building upon traditional concepts of cancer and stem cells, this model is intended to shed new light on the continuing struggle with treatment challenges such as tumor drug-resistance and recurrence. This review describes the cancer stem cell model with an emphasis on delineating markers that represent a "stemness" phenotype within certain tumor cells. The objective of this delineation is to develop targeted therapies for the selective elimination of cancer stem cells with minimal toxicity to normal stem cells and tissues. However, this specific targeting of cancer stem cells has proved to be a significant challenge due to the similarity of markers expressed by both normal and cancer stem cells. Still, research in the area of cancer biomarkers is steadily progressing.