There were other surprises as well. DNA methylation in cancer was discovered about 10 years ago and until now, people believed that its role in cancer was limited to inactivating tumor-suppressor genes. The genes represented by this 40 percent should be investigated for their relationship to cancer. The function of those genes whose activation remains unchanged by methylation is unclear, though, as are the consequences of this methylation for the cell. We believe that methylation may contribute to the overall genetic instability in the tumor.
Genetic instability refers to the ease with which malignant cells can develop additional mutations.
The researchers also found that the pattern of methylation was very specific for some types of tumors. Aberrant DNA methylation may therefore provide a way to identify subtypes of cancer that respond better to certain kinds of treatment. Plass said there is also preliminary evidence suggesting that resistance to chemotherapy is in some cases linked to the degree of aberrant methylation in some tumors. The study, conducted by Plass and a large team of researchers, examined 98 tumor samples to determine if any of the islands were methylated. How DNA methylation turns off genes, and why it goes wrong in cancer cells is still unknown.