What Causes Cancer? Most, if not all cancers are caused and perpetuated by a small population of tumor-initiating cells that exhibit numerous stem cell-like properties. Adult stem cells (SC) are involved in the regeneration and maintenance of our body tissues and account for one out of every 6 million cells. Each tissue has a unique population of specific SCs located in regions known as niches. In the SC niche, the SCs exist in a unique dormant state known as quiescence, and remain in this state until they are given the cues to be activated. Activated stem cells go through two stages of development referred to as proliferation and differentiation. During proliferation, biochemical cues cause the cells to reproduce, resulting in an expanded population of similar cells. Differentiation puts a stop to proliferation with specific biochemical cues that cause the proliferating cells to differentiate into a specific type of cell. Once a stem cell has differentiated, it has a finite life span