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Recent incidence patterns of cutaneous T-cell lymphoma (CTCL) in the US are not well described. We sought to describe recent incidence trends by tumor subtype, sex, age, race and ethnicity, socioeconomic status (SES), and geography.

Incidence data were derived from 18 population-based registries of the Surveillance, Epidemiology, and End Results (SEER) Program for 2000 to 2018. We included histologically confirmed cases of first primary CTCL with malignant behavior and primary site of involvement skin (C44.0-C44.9). Patient characteristics included sex, age, race and ethnicity, and geographic region (metropolitan vs nonmetropolitan counties).¹ Area-level SES information was available from 2000 to 2016 and was categorized into quintile; Q1 lowest, Q5 highest.² We used the 2000 US standard population to calculate age-adjusted annual incidence rates (IR) per million people. Annual percent change (APC) was calculated by using the weighted least squares method. Statistical calculations used SEER*Stat statistical software (version 8.3.9.2) in January 2022. The Stanford institutional review board deemed this study exempt from review and waived the requirement for patient informed consent because only deidentified data were used.

We identified 14 942 new cases of CTCL from 2000 to 2018. Table 1 shows the number of cases, IR, and APC of IR of CTCL by International Statistical Classification of Diseases and Related Health Problems for Oncology (ICD-O) diagnosis. Mycosis fungoides (MF) was the most common diagnosis, followed by primary CTCL (PCTCL) and primary cutaneous anaplastic large cell lymphoma (PCALCL). The overall CTCL incidence was 8.55 per million and increased over the study period (APC, 0.61%). Among CTCL subtypes, MF had the highest incidence (5.42) and Sézary syndrome had the highest increase (APC, 3.83%). Overall, PCTCL was the only subtype with decreasing incidence over the study period (APC, −1.39%).

Table 2 shows IR and APC by tumor subtype, sex, age, race and ethnicity, SES, and geographic region. Overall, CTCL incidence was highest in men (10.06), non-Hispanic Black patients (11.68), individuals in highest SES quintiles (10.31), and patients living in metropolitan counties (8.96). Patients aged 40 years or older had a 6-times higher overall incidence rate than those younger than 40 years. Despite having a lower incidence compared with the older age group, patients younger than 40 years showed significantly higher increases in overall CTCL IR (APC, 2.87%) and in MF IR (APC, 3.67%). Other groups with significant increases in incidence included women (APC, 0.92%), non-Hispanic Black patients (APC, 1.63%), patients in the lowest SES quintile (APC, 1.87%), and individuals in metropolitan counties (APC, 0.68%).

We observed an increased overall CTCL incidence between 2000 and 2018. These findings differ from previous North American studies,^3,4 which suggested CTCL incidence stabilized after 1998, but are consistent with recent studies from Europe.⁵ These trends are likely multifactorial. Better diagnostic tools and increased awareness among physicians and patients may have led to improved CTCL detection. Physician density has been associated with higher incidence⁶; therefore, efforts to increase access to health care may contribute to a rise in CTCL diagnosis. The incidence of PCTCL has decreased considerably since 2000, possibly owing to better classification because PCTCL is often a diagnosis of exclusion.

Overall, CTCL incidence by age, sex, and race and ethnicity stayed mostly consistent with previous reports.^1,6 One key new finding is the more rapid increase in incidence among young patients, possibly owing to earlier diagnosis. Another hypothesis is that MF cases previously misdiagnosed as atopic dermatitis or psoriasis are discovered at a younger age in the era of biologics. Higher SES and metropolitan county were both associated with increased incidence, consistent with previous studies⁶ correlating with income and physician density. Environmental exposures may also be associated with CTCL owing to clustering of cases in industrial regions of North American cities.⁴

To our knowledge, this is the first study to analyze CTCL incidence by SES and geography. Limitations include potential underreporting, heterogeneous classification, changes in diagnostic tools, and small sample sizes.

These findings suggest that the incidence of CTCL continues to increase in the US. Prospective data collection efforts should gather data on SES, geographic location, and health care access to better understand these differences.

Accepted for Publication: June 8, 2022.

Published Online: September 1, 2022. doi:10.1001/jamaoncol.2022.3236

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2022 Cai ZR et al. JAMA Oncology.

Corresponding Author: Eleni Linos, MD, DrPH, Department of Dermatology, Stanford University School of Medicine, 269 Campus Dr, Stanford, CA 94305 (linos@stanford.edu).

Author Contributions: Zhuo Ran Cai and Eleni Linos had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Cai, Chen, Weinstock, Novoa, Linos.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Cai, Linos.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Cai, Chen, Linos.

Obtained funding: Linos.

Administrative, technical, or material support: Linos.

Supervision: Kim, Novoa, Linos.

Conflict of Interest Disclosures: None reported.

Funding/Support: Dr Linos is supported by the National Institutes of Health (NIH) (grants DP2CA225433 and K24AR075060). Dr Novoa is supported by the Melanoma Research Alliance’s L’Oreal Dermatological Beauty Brands-MRA Team Science Award.

Role of the Funder/Sponsor: The funding agencies had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Disclaimer: The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.