Lymphoma incidence patterns by WHO subtype in the United States, 1992-2001.

Because the causes of most lymphoid neoplasms remain unknown, comparison of incidence patterns by disease subtype may provide critical clues for future etiologic investigations. We therefore conducted a comprehensive assessment of 114,548 lymphoid neoplasms diagnosed during 1992-2001 in 12 Surveillance, Epidemiology, and End Results (SEER) registries according to the internationally recognized World Health Organization (WHO) lymphoma classification introduced in 2001. Cases coded in International Classification of Diseases for Oncology, Second Edition (ICD-O-2), were converted to ICD-O-3 for WHO subtype assignment. Age-specific and age-adjusted rates were compared by sex and race (white, black, Asian). Age-adjusted trends in incidence were estimated by sex and race using weighted least squares log-linear regression. Diverse incidence patterns and trends were observed by lymphoid neoplasm subtype and population. In the elderly (75 years or older), rates of diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma increased 1.4% and 1.8% per year, respectively, whereas rates of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) declined 2.1% per year. Although whites bear the highest incidence burden for most lymphoid neoplasm subtypes, most notably for hairy cell leukemia and follicular lymphoma, black predominance was observed for plasma cell and T-cell neoplasms. Asians have considerably lower rates than whites and blacks for CLL/SLL and Hodgkin lymphoma. We conclude that the striking differences in incidence patterns by histologic subtype strongly suggest that there is etiologic heterogeneity among lymphoid neoplasms and support the pursuit of epidemiologic analysis by subtype.