In a variety of tumors, such as breast cancer, lung cancer, colorectal cancer, pancreatic cancer, gastric cancer, and cervical cancer, the expression of DNMT3B is often upregulated,177 and this upregulation is associated with enhanced tumor cell proliferation, migration, and invasive capacity.178 For example, in AML, mutations in DNMT3B can lead to changes in de novo DNA methylation patterns, affecting gene expression and boosting the occurrence and development of leukemia.179 However, in some cases, the downregulation or loss of function of DNMT3B is also related to the occurrence of tumors. The gene discussed is DNMT3B; the disease is gastric cancer.