Incidence of extranodal non-Hodgkin lymphomas among whites, blacks, and Asians/Pacific Islanders in the United States: anatomic site and histology differences.

BACKGROUND: Extranodal non-Hodgkin lymphoma (NHL) accounts for much of the increase in NHL incidence in the past three decades in the United States, but its descriptive epidemiology is scarce in the literature.

METHODS: Incidence data for the years 1999-2003 were from 38 population-based cancer registries, covering 82% of US population. We grouped anatomic sites of extranodal NHLs according to the Surveillance, Epidemiology, and End Results (SEER) site recodes, and histology subtypes according to the nested classification of lymphoid neoplasms developed by the Pathology Working Group of the International Lymphoma Epidemiology Consortium.

RESULTS: Blacks and Asians/Pacific Islanders (APIs) experienced incidence rates about the same as or lower than whites' for B-cell extranodal NHL as a whole and most of its histologic subtypes. The significant exceptions are: API men had a 40% higher rate of marginal zone lymphoma (MZL) than white men, and API women had a 12% higher rate of diffuse large B-cell lymphoma (DLBCL) than white women. The rates of all T-cell extranodal NHLs combined and peripheral T-cell lymphoma (PTCL) among black women exceeded those of white women by 46% and 18%, respectively. Blacks also had higher rates of mycosis fungoides (MF) than whites (28% higher for men and 99% higher for women). The most common sites of extranodal NHL are stomach, skin, and oral cavity and pharynx. Compared with whites, blacks had either lower or similar incidence of NHL for all sites except skin for women while APIs had higher rates of NHL of the stomach, nose/nasal cavity/middle ear, colorectum (women only), and brain (men only). Age was associated with race- and sex-specific differences in histology-specific incidence rates.

CONCLUSION: While blacks and APIs had lower or similar overall incidence rates for extranodal NHL, they experienced excessive rates in some subtypes. Blacks had higher rates of the two most common types of T-cell extranodal NHL and APIs had higher rate of the two common types of B-cell types than whites. Distinct race-specific patterns in histology- and site-specific incidence of extranodal NHL may implicate racial differences in risk factor exposure and/or genetic predisposition.