Primary malignant nervous system neoplasms. Birth cohort effect in the elderly.

Current data indicate that mortality for primary malignant nervous system neoplasms (NSNs) provides a fairly accurate index of incidence. Average annual age- and sex-specific death rates among whites for primary malignant NSNs in the 48 contiguous United States from 1940 through 1975 showed a marked cohort effect among the elderly of either sex. For white men aged 60 through 64 years, mortality increased steadily from 5.3 per 100,000 per year for those born in 1880 to 16.1 per 100,000 per year for the 1910 cohort. No definite cohort effect was seen in the young. The increase in mortality could be due to better diagnosis and more complete case ascertainment for deaths due to primary malignant NSNs, but further studies are required to distinguish a real from an artifactual increase in mortality.