Stem Cells and the Side Population Theory: A Critical Review

This review provides an overview of the Side Population (SP) phenotype related to stemness biology and tumorigenesis, highlighting the key technical mechanisms and biological processes involved. The actual challenges to fully exploit the possibilities provided by the SP phenotype in normal and cancer tissues are discussed. We put forward some suggestions for future research and the empowerment of a network of SP users to make the SP assay fully understood and technically scalable for its broader use.