When cancer patients accumulated in one pedigree, the cancer is named as familial cancer. Especially when there is strong genetic background, It is named as hereditary cancer. Most of them are caused by genetic mutation in a gene related to cancer susceptibility. The gene is classified among suppressor oncogenes, oncogenes or DNA repair genes. Although hereditary cancer is uncommon, genetic testing is very useful to confirm hereditary cancer and to diagnose it in the presymptomatic stage. On the other hand, it poses ethical problems, therefore a strategy including genetic counseling is essential.