Overexpression of B lymphoma Moloney murine leukemia virus insertion region-1 (BMI1), a transcription repressor that operates in stem cell maintenance and oncogenesis through inhibition of INK4A/ARF tumor suppressor locus, has been linked with increased incidence of metastasis in human gastric and breast cancer, as well as melanoma and other cancer types. This evidence concerns the gene CDKN2A and breast cancer.