Emerging epidemiological trends in primary cutaneous lymphomas: a population-based analysis

BACKGROUND: Primary cutaneous lymphomas (PCLs), comprising cutaneous T-cell lymphomas (CTCLs) and cutaneous B-cell lymphomas (CBCLs), are rare non-Hodgkin lymphomas with distinct epidemiological characteristics. How the incidence rates (IRs) of PCLs have changed over the past decade has not been well documented. OBJECTIVES: To assess changes in IRs in overall and subtype-specific PCLs in the USA by sex, age and ethnic group. METHODS: This study analysed 13 126 cases of PCL diagnosed between 2010 and 2021 using data from the Surveillance, Epidemiology and End Results programme. Age-adjusted IRs (aaIRs), 5-year relative survival and annual percentage change were calculated. RESULTS: The overall aaIR of PCLs was 11.9 per 1 000 000 person-years, with 8.8 for CTCLs and 3.1 for CBCLs. Among CTCL subtypes, mycosis fungoides had the highest aaIR of 5.2, whereas within CBCLs, primary cutaneous marginal zone lymphoma exhibited the highest aaIR of 1.4. Between 2014 and 2021, the aaIR of CBCLs declined annually by 4.9%. In males, aaIRs for CTCLs and CBCLs decreased by 3.5% and 4.8%, respectively, per year over the same period. Five-year relative survival was 89.3% for CTCLs and 91.5% for CBCLs. CONCLUSIONS: The incidence of PCLs has exhibited distinct patterns of decline among different population groups over the past decade. The continued disparities in both incidence and survival underscore the need for targeted research and interventions to mitigate demographic inequalities.