The findings, which contradict prior North American studies, suggest that the incidence rate of the rare cancer continues to increase in the United States.
Cutaneous T-cell lymphoma (CTCL) is a rare cancer, but a research letter published in JAMA Oncology shows that the overall incidence of CTCL in the United States has increased over time—findings that are contrary to other North American studies but that mirror recent European study findings.
Data from 18 population-based registries within the Surveillance, Epidemiology, and End Results Program were used in the study. Histologically confirmed primary CTCL cases with skin as the primary site of involvement were included in the analysis, as were data from 2000 to 2018. Information on patient age, sex, race and ethnicity, and geographic region were available, with area-level socioeconomic status (SES) information from 2000 to 2016 also available and separated into quintiles.
The age-adjusted annual incidence rates per 1 million people were calculated based on the 2000 US standard population, and annual percentage change (APC) was calculated with the weighted least squares method.
A total of 14,942 CTCL cases were identified between 2000 to 2018, with mycosis fungoides (MF), primary CTCL (PCTCL), and primary cutaneous anaplastic large cell lymphoma being the most common diagnoses. The overall incidence rate of CTCL was 8.55 per 1 million, and it increased over the study period, with an APC of 0.61%. MF had the highest incidence out of the CTCL subtypes in the analysis, at 5.42 per 1 million and Sézary syndrome showed the highest increase with an APC of 3.83%; the only subtype to decrease over time was PCTCL with an APC of –1.39%.
Men, non-Hispanic Black patients, individuals in the highest SES quintiles, and patients in metropolitan counties had the highest overall CTCL incidences (10.06, 11.68, 10.31, and 8.96 per 1 million, respectively). Women, non-Hispanic Black patients, patients in the lowest SES quintiles, and individuals in metropolitan counties showed significant increases in incidence over time (APCs of 0.92%, 1.63%, 1.87%, and 0.68%, respectively).
The overall incidence rate for patients 40 years or older was 6 times higher than the IR in patients younger than 40 years. However, patients younger than 40 years had more significant increases in CTCL IR (APC, 2.87%) and MF IR (APC, 3.67%) over the study period than patients aged 40 or older.
The increase in IR among younger patients is notable, and the authors hypothesize that cases previously misdiagnosed as atopic dermatitis or psoriasis might be identified in younger patients due to advances in biologics.
The continual increase in CTCL incidence through 2018 in the study is in line with recent European studies but contradicts prior North American studies, and the authors pose several factors that may contribute to the higher incidence of CTCL.
“Better diagnostic tools and increased awareness among physicians and patients may have led to improved CTCL detection,” the authors wrote. “Physician density has been associated with higher incidence; therefore, efforts to increase access to health care may contribute to a rise in CTCL diagnosis.”
Higher SES and living in a metropolitan county both correlated with increased incidence in the study, which parallels previous studies associating income and physician density.
“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,” the authors concluded.
Cai ZR, Chen ML, Weinstock MA, Kim YH, Novoa RA, Linos E. Incidence trends of primary cutaneous T-cell lymphoma in the US from 2000 to 2018: a SEER population data analysis. JAMA Oncol. Published online September 1, 2022. doi:10.1001/jamaoncol.2022.3236