Incidence of Cutaneous T-Cell Lymphoma in the United States, 1973-2002

OBJECTIVE: To describe incidence trends for cutaneous T-cell lymphoma (CTCL) in the United States. DESIGN: Population-based study. SETTING: Data were obtained from 13 population-based cancer registries of the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute from 1973 through 2002. PARTICIPANTS: A total of 4783 cases of CTCL were identified for the period 1973 through 2002. MAIN OUTCOME MEASURE: Diagnosis of CTCL. RESULTS: The overall annual age-adjusted incidence of CTCL was 6.4 per million persons. Annual incidence increased by 2.9 x 10(-6) per decade over the study period. Incidence was higher among blacks (9.0 x 10(-6)) than among whites (6.1 x 10(-6)) and was higher among men (8.7 x 10(-6)) than among women (4.6 x 10(-6)). The racial differences in incidence decreased with age, while the sex differences increased with age and decreased over time. Substantial geographic variation in incidence was found. Incidence was correlated with high physician density, high family income, high percentage of population with a bachelor's degree or higher, and high home values. Changes in International Classification of Diseases for Oncology (ICD-O) morphologic definitions have resulted in the redistribution of the cases of CTCL among specific subclassifications. CONCLUSIONS: The continued rise in incidence of CTCL is substantial, and the cause of this increase is unknown. The racial, ethnic, sex, and geographic differences in incidence may be of etiologic importance. Changes in ICD-O definitions have made it difficult to evaluate incidence trends for subclassifications of CTCL such as mycosis fungoides. In addition, these changes resulted in the creation of ambiguous histologic codes, which may have caused coding errors. These errors along with the lack of independent verification are limitations of our study. An epidemiological investigation using population-based data is important to better understand this disorder.