Abstract

It has been widely accepted that most human cancers had a small subpopulation of cancer stem cells (CSCs) which were closely related to progenitor stem cells (PSCs) based on cell features and biological missions. These cells express ATP binding cassette drug pump that can effectively exclude toxic materials and have activation of anti-apoptosis programs that negate the pro-apoptotic signals activated by DNA damaging agents [1-4]. Thus, these cells are resistant to cytotoxic drugs and radiation. These cells normally reside in acidic and hypoxic microenvironment hard to reach by the blood stream. Like PSCs, CSCs may remain dormant unless situations arise that stimulate their recruitment, such as cytotoxic chemotherapy.