Background: Significant advances in the understanding of non-Hodgkin's lymphoma (NHL) have occurred in the past two decades, resulting in changes in terminology and classification practices, which may affect the analysis of the Surveillance, Epidemiology, and End Results (SEER) data.
Methods: The incidence rates for each subgroup of NHL in the Working Formulation were reviewed from the National Cancer Institute's SEER data during three time periods: 1973-1977, 1978-1982, and 1983-1987.
Results: NHL has significantly increased by 50% from 1973 to 1988. The most frequently occurring NHL is diffuse large cell lymphoma, constituting nearly 30% of all lymphomas. Increased incidence rates for large cell immunoblastic and small noncleaved cell NHL observed during the 1980s are attributable largely to the acquired immunodeficiency syndrome epidemic. Exposure to environmental agents such as herbicides and hair coloring dyes have recently been identified as factors that increase the risk of NHL, but the overall contribution of these factors remains to be identified. The increase in extranodal lymphomas is in part a consequence of the application of modern immunophenotypic and genotypic methods, which lead to the reclassification of pseudolymphomas as monoclonal B-cell neoplasms. The apparent dramatic decline in the incidence of diffuse small cleaved NHL appears to be artifactual, as well, secondary to changes in classification of NHL.
Conclusions: With the enhanced ability of pathologists to delineate new clinicopathologic entities by immunophenotypic and molecular biologic studies, future modifications to the collection of SEER data may be appropriate. Such an approach will address the limitations of the Working Formulation and lead to a more accurate data base for the evaluation of epidemiologic trends.