Mediator subunits also play a role in tumorigenesis, as shown for CDK8, which acts as an oncogene regulating β-catenin activity in colorectal cancer [27], MED12, where mutations occur in uterine leiomyomas and prostate cancer [28, 29], and MED29, which has been implicated as an oncogene as well as tumor suppressor in pancreatic cancer [30]. The gene discussed is MED12; the disease is uterine corpus leiomyoma.