Tumors and aging: the influence of age-associated immune changes upon tumor growth and spread.

Abstract

There has been a clinical impression that tumors are less malignant in older people. Such has been claimed for breast, colon, prostate and lung carcinomas (Schottenfield and Robbins, 1971; Berkson et al., 1957, Calabrese et al., 1973; Ershler et al., 1983; Pickren et al., 1982; Suen et al., 1974). The great heterogeneity in clinical populations, confounded by antecedent illness, medicines, exposures, and social circumstances have precluded a statistical confirmation of such age-associated changes. Nonetheless, in experimental animals, ’we and others have found significant differences in tumor growth and spread when the common variable is host age. Weakly immunogenic tumors such as B16 melanoma or Lewis lung carcinoma (3LL) growrnore slowly in old mice, but more immunogenic tumors such as methylcholanthrene-induced fibrosarcomas grow more rapidly. We have explored a variety of proposed mechanisms for the observed differences and have concluded that the age-associated decline in immune function (immune senescence) is central to the reduced aggressiveness of weakly antigenic tumors in older hosts.