The genetic and environmental factors contributing to initiation and growth of uterine leiomyoma tumors Somatic mutations of the stem cell population are thought to have a major role in initiation of tumors while the subsequent phenotype, and progression is influenced by environmental and epigenetic factors. miRNA, microRNA; RANKL, receptor activator of NF-κB; TGFβ, transforming growth factor β; Wnt, wingless related integration site.