[Aging and development, growth and spreading of cancer]

In spite of steep elevation of cancer mortality in the aged, it has been believed that ageing reduces susceptibility to carcinogens. Ebbesen, however, presented contradictory result recently. We examined influences of ageing on chemical carcinogenesis using 6 different age groups of rats given N-bis (2-hydroxypropyl) nitrosamine (DHPN). The results suggested (1) susceptibility to initiating process did not differ much, but promoting process might be prolonged in aged rats, and (2) susceptibility difference was enlarged in aged individuals. These data were supported by doubling time of lung tumors. Another evidence suggesting retarded tumor growth in the aged was observed in frequency of organ metastasis of gastric cancer. The conspicuous finding was shown in the number of cases of gastric cancer without any organ metastasis, i.e. 42.3% in the aged male and 9.3% in the younger male. Occurrence of lymphangitis carcinomatosa in the lung also showed distinct difference between the aged and the younger groups. This type of metastasis mostly derived from gastric cancer, especially signet ring cell cancer. Degree of differentiation of developed tumor may be another point of consideration to estimate the age dependency of tumor metastasis. We also have to pay some attention to the cancers increasing with age.