Monoclonality refers to a group of cells having a single cell as their origin, whereas polyclonality suggests that a mass of tissue is composed of several cell populations having arisen from different progenitor cells. Numerous compelling experiments have provided evidence that cancer is a monoclonal. For example, lineage tracing studies following X-chromosome inactivation patterns in leiomyomas in women heterozygous for the glucose-6-phosphate (G6PD) gene, encoded on the X-chromosome, found that cells within the tumor all expressed the same form of G6PD. Suggesting they all had descended from a single cell which only expressed that particular X-chromosome. Further studies on cancers presenting with translocations within their karyoptype have