Much remains unknown about the role of epigenetic factors and cancer. Epigenetic changes are reversible modifications to genes or proteins that occur in the tumor and its microenvironment. Epigenetic modifier molecules have been observed making tumor-friendly, nonmutational changes in an already confused biosystem. For example, by heavily methylating genes or promoter regions, gene activity critical to counteract a tumor's drive toward metastasis gets turned off. Or noncoding ribonucleic acids meddle in epigenetic fashion, interfering with a cell's regulation of growth or attempt to repair damage.