A 59-year-old man complains of progressive weakness. He reports that his stools are very dark. Physical examination demonstrates fullness in the right lower quadrant. Laboratory studies show iron deficiency anemia, with a serum hemoglobin level of 7.4 g/dL. Stool specimens are positive for occult blood. Colonoscopy discloses an ulcerating lesion of the cecum. Laboratory studies of the surgical specimen obtained from the patient demonstrate hypermethylation of the p53 gene. Which of the following best characterizes this biochemical change in the neoplastic cells?

Hypermethylation of many tumor suppressor and DNA repair genes has been demonstrated in human tumors. The pathways controlled by these genes are, therefore, suppressed. For example, the normal p53 gene can be inactivated by hypermethylation. Thus, aberrant methylation of tumor suppressor genes may be an epigenetic mechanism for a "second hit," leading to loss of heterozygosity Unlike genetic changes in cancer, epigenetic changes are reversible, and a search for drugs that influence DNA methylation is under way. The other choices are unrelated to DNA methylation.Diagnosis: Colon cancer