Up to 5% of cancer patients fall under hereditary tumor syndromes, and they are in a state of high cancer susceptibility, mainly due to autosomal dominant inheritance. For some hereditary tumors, it has become possible to propose new preventive measures for pre-onset cancer (primary prevention to inhibit the onset of cancer, and secondary prevention to detect cancer early and prevent it from becoming severe) to people who have developed cancer or have not yet developed cancer, based on the guidelines. Women with hereditary cancer syndromes have an increased risk of developing endometrial cancer, which is mainly associated with germline heterozygous pathogenic variants of DNA mismatch repair genes of Lynch syndrome and PTEN of Cowden syndrome. It is predicted that the number of patients diagnosed with hereditary tumor syndromes will simultaneously increase because the number of treatments for which testing of mismatch repair protein deficiency or microsatellite instability will be used as companion diagnostics will increase in the future. Growing evidence indicates that diagnostic genetic testing is useful to find asymptomatic carriers of pathogenic variants and propose appropriate surveillance for secondary prevention. Conversely, there is still limited evidence for primary prevention of hereditary endometrial cancer.