The occurrence of malignant neoplasms increases with advancing age. Although aging and carcinogenesis are basically different processes, there are phenomena common to each such as accumulation of DNA damage and abnormal proteins, telomere shortening, and dysfunction of immune and metabolic systems. Common cancers in the elderly are gastric, lung, colorectal and prostate cancers in men whereas colorectal, gastric, lung and biliary cancers in women. Compared with malignant neoplasm in the younger patients, there exist several characteristic features such as tumor location, histology, biological behavior and pathway of carcinogenesis in tumors occurring in the elderly. The representative tumors are as follows: solid-type poorly differentiated adenocarcinoma occurring in the gastric antrum, microsatellite-unstable medullary and mucinous colorectal carcinomas, proximal colon carcinomas, squamous cell carcinoma of the lung, apocrine and mucinous carcinoma of the breast, hepatocellular carcinoma without cirrhosis, acute myeloid leukemia arising from myelodysplastic syndrome, and intraductal papillary-mucinous neoplasm of the pancreas. These tumors may have different pathways of carcinogenesis in comparison with those in the younger patients. Multiple cancers also increase with aging. Although it is generally recognized that carcinoma in the elderly shows well differentiation, slow growth, low incidence of metastasis and favorable prognosis, the tumor does not always show such features. Regarding biological behavior of malignant tumor in the elderly, age-related alterations of the host such as stromal weakness and decreased immune response against cancer cell invasion should be considered as well as characteristics of tumor cell itself.