NON-HODGKINS-LYMPHOMA

Background. Significant advances in the understanding of non-Hodgkin's lymphoma (NHL) have occurred in the past two decades, resulting in ch anges in terminology and classification practices, which may affect th e analysis of the Surveillance, Epidemiology, and End Results (SEER) d ata. Methods. The incidence rates for each subgroup of NHL in the Work ing Formulation were reviewed from the National Cancer Institute's SEE R data during three time periods: 1973-1977, 1978-1982, and 1983-1987. Results. NHL has significantly increased by 50% from 1973 to 1988. Th e most frequently occurring NHL is diffuse large cell lymphoma, consti tuting nearly 30% of all lymphomas. Increased incidence rates for larg e cell immunoblastic and small noncleaved cell NHL observed during the 1980s are attributable largely to the acquired immunodeficiency syndr ome epidemic. Exposure to environmental agents such as herbicides and hair coloring dyes have recently been identified as factors that incre ase the risk of NHL, but the overall contribution of these factors rem ains to be identified. The increase in extranodal lymphomas is in part a consequence of the application of modern immunophenotypic and genot ypic methods, which lead to the reclassification of pseudolymphomas as monoclonal B-cell neoplasms. The apparent dramatic decline in the inc idence 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 e ntities by immunophenotypic and molecular biologic studies, future mod ifications to the collection of SEER data may be appropriate, Such an approach will address the limitations of the Working Formulation and l ead to a more accurate data base for the evaluation of epidemiologic t rends.