DNA hypomethylation is a common epigenetic change in cancer, first recognized in 1983. It was initially overlooked compared to hypermethylation of tumor suppressor genes. Recent studies show that DNA hypomethylation is frequently associated with hypermethylation in cancer, often in different sequences. DNA hypomethylation in cancer is not an anomaly but a common feature. It is linked to cancer stem cells and has biological and clinical significance. DNA hypomethylation can occur early in carcinogenesis and is associated with tumor progression. It is often found in repeated DNA sequences, which make up half of the genome. Hypomethylation of these sequences contributes to global DNA hypomethylation in cancer. Hypomethylation of gene regions is less frequent than hypermethylation of CpG islands. Some genes, such as cancer-testis genes, are hypomethylated in cancer. Hypomethylation of DNA is more pronounced with tumor progression. DNA hypomethylation is associated with the grade of cervical neoplasia, multifocal hepatocellular carcinomas, and breast tumor characteristics. It is also linked to lymph node involvement in prostate cancer and postoperative recurrence in hepatocellular carcinomas. DNA hypomethylation is a significant marker for relapse and survival in ovarian cancer. DNA hypomethylation is dynamic and can be influenced by environmental factors. It is also associated with other diseases and normal development. DNA hypomethylation can be a cause of cancer, as shown by studies in mouse models. It is linked to the formation and progression of tumors. DNA hypomethylation can affect gene expression by altering the sequestration of transcription control proteins. It is also involved in chromosomal rearrangements and transposable element activation. DNA hypomethylation is a key factor in cancer progression and is associated with the origin of cancer stem cells. Active DNA demethylation occurs in cancer and is not just passive. It involves mechanisms such as DNA glycosylase activity and oxidative deamination. DNA demethylation can spread in cis and is associated with the formation of hemimethylated intermediates. It is also linked to the development of cancer and the progression of tumors. DNA demethylation is a dynamic process and is influenced by various factors, including microRNAs and chromatin remodeling. It is a key factor in cancer and has implications for diagnosis and treatment.DNA hypomethylation is a common epigenetic change in cancer, first recognized in 1983. It was initially overlooked compared to hypermethylation of tumor suppressor genes. Recent studies show that DNA hypomethylation is frequently associated with hypermethylation in cancer, often in different sequences. DNA hypomethylation in cancer is not an anomaly but a common feature. It is linked to cancer stem cells and has biological and clinical significance. DNA hypomethylation can occur early in carcinogenesis and is associated with tumor progression. It is often found in repeated DNA sequences, which make up half of the genome. Hypomethylation of these sequences contributes to global DNA hypomethylation in cancer. Hypomethylation of gene regions is less frequent than hypermethylation of CpG islands. Some genes, such as cancer-testis genes, are hypomethylated in cancer. Hypomethylation of DNA is more pronounced with tumor progression. DNA hypomethylation is associated with the grade of cervical neoplasia, multifocal hepatocellular carcinomas, and breast tumor characteristics. It is also linked to lymph node involvement in prostate cancer and postoperative recurrence in hepatocellular carcinomas. DNA hypomethylation is a significant marker for relapse and survival in ovarian cancer. DNA hypomethylation is dynamic and can be influenced by environmental factors. It is also associated with other diseases and normal development. DNA hypomethylation can be a cause of cancer, as shown by studies in mouse models. It is linked to the formation and progression of tumors. DNA hypomethylation can affect gene expression by altering the sequestration of transcription control proteins. It is also involved in chromosomal rearrangements and transposable element activation. DNA hypomethylation is a key factor in cancer progression and is associated with the origin of cancer stem cells. Active DNA demethylation occurs in cancer and is not just passive. It involves mechanisms such as DNA glycosylase activity and oxidative deamination. DNA demethylation can spread in cis and is associated with the formation of hemimethylated intermediates. It is also linked to the development of cancer and the progression of tumors. DNA demethylation is a dynamic process and is influenced by various factors, including microRNAs and chromatin remodeling. It is a key factor in cancer and has implications for diagnosis and treatment.