Cutaneous T-cell lymphomas are a heterogeneous group of cancers. Some subtypes of cutaneous T-cell lymphomas are often misdiagnosed as benign skin diseases, making it challenging to gather reliable epidemiologic data.
At the 3rd World Congress of Cutaneous Lymphomas (sponsored by the International Society for Cutaneous Lymphomas), experts updated attendees on temporal trends in cutaneous T-cell lymphomas and prevention efforts, acknowledging that these areas of study are hampered by the heterogeneity of the disease, its relative rarity, and the lack of standardized definitions.
A study is only as good as the data. As epidemiologists, we need to be able to measure the reliability of what we are reporting, and that has been lacking so far.— Martin Weinstock, MD, PhD
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“There are controversies and ambiguities about the terminology for cutaneous T-cell lymphomas. Even though there are accepted definitions of cutaneous T-cell lymphomas, this is not sufficient. Agreement on these definitions has to extend to the broad community and to registries,” noted Martin Weinstock, MD, PhD, of the Warren Alpert Medical School of Brown University, Providence, Rhode Island, who reported on the temporal trends in the incidence of cutaneous T-cell lymphomas.1
“Classification of cutaneous T-cell lymphomas has changed over the past 25 years. Now we know there are T-cell and B-cell subtypes, which further stymies our ability to track cutaneous T-cell lymphomas,” Dr. Weinstock told listeners.
His presentation was based on data from nine common Surveillance, Epidemiology, and End Results (SEER) registries, showing that the incidence of cutaneous T-cell lymphomas increased from 1973 to 2000 and plateaued from 2000 on. From 1973 to 1978, the number of diagnoses of cutaneous T-cell lymphomas increased by almost 6% per year. Since then, the increase has been negligible.
The male-to-female ratio has also changed over the same time period. In the 1970s, the male-to-female ratio was 2:3; in 2000 to 2004, it was 1:7, and from 2005 to 2009, it was 1:6.
“There are differences in socioeconomic correlations, with markedly different rates in San Jose vs San Francisco, for example. The reasons for these differences are not clear,” Dr. Weinstock noted.
A More Accurate Picture
Another challenge to quantifying the number of cases of cutaneous T-cell lymphomas is that mycosis fungoides, the most common type of cutaneous T-cell lymphoma, often masquerades as psoriasis or other benign skin diseases. With currently used technology, mycosis fungoides cannot be reliably distinguished from non–mycosis fungoides. From 1990 to 2001, the rate of cutaneous T-cell lymphomas not otherwise specified was 8.5 per 100,000, whereas the rate of mycosis fungoides during that period was 1 per 100,000.
“We know that a certification bias leads to underreporting of deaths coded as cutaneous T-cell lymphomas by more than 50%. We need standardized definitions to gain a more accurate picture,” he stated.
“Mortality associated with cutaneous T-cell lymphomas is underestimated, and many questions remain unanswered,” Dr. Weinstock said.
Temporal patterns in the incidence of cutaneous B-cell lymphomas are similar over the same time periods, according to the SEER database. The incidence increased from 1973 until around 2000. From 1973 to 2003, the annual percentage change in the diagnosis of cutaneous B-cell lymphomas increased by 7% per year, and after 2003, there was no change.
“The incidence of cutaneous B-cell lymphomas has stabilized since 2003, and now there are about four new cases per million per year,” Dr. Weinstock said.
Efforts at Prevention
There is a large epidemiology literature on non-Hodgkin lymphoma, but little of it applies to cutaneous T-cell lymphomas. Studies do not separate the data based on histologic subtype, and classification systems have changed.— Steven D. Stellman, PhD, MPH
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Because cutaneous T-cell lymphomas are relatively rare and quite heterogeneous, it has been challenging to identify risk factors to inform primary prevention strategies, explained Steven D. Stellman, PhD, MPH, of Mailman School of Public Health, Columbia University, New York.
“Geographic variability can provide clues about cutaneous T-cell lymphomas,” he noted, “but most epidemiology studies have lumped cutaneous T-cell lymphomas in with other lymphomas. There is a large epidemiology literature on non-Hodgkin lymphoma, but little of it applies to cutaneous T-cell lymphomas. Studies do not separate the data based on histologic subtype, and classification systems have changed. On the other hand, subdividing cutaneous T-cell lymphomas into subtypes reduces the statistical power of the data,” Dr. Stellman explained.
Development of prevention strategies requires correlations between occupations and exposures in cutaneous T-cell lymphomas cases. Exposures are more difficult to measure than occupations, Dr. Stellman admitted.
The best guesstimates of exposures related to the development of cutaneous T-cell lymphomas are extrapolated from the non-Hodgkin lymphoma (NHL) literature. Known, suspected, and disputed exposures related to NHL include retroviruses, herpes virus, Helicobacter pylori, and infectious diseases of childhood; radiation and ultraviolet light exposure; and diets rich in trans-unsaturated fat with little intake of fruits and vegetables. Occupations linked to NHL include farming, forestry, pulp and paper manufacturing, rubber manufacturing, animal breeding, and hairdressing.
A study of survivors of the World Trade Center tragedy who developed NHL implicated exposure to organochlorine pesticides, polychlorinated biphenyl compounds, herbicides, industrial solvents, tetrachlorethylene, paint thinner, benzenes, and dioxins.
“These studies looked at NHL as a specific disease outcome. Small studies in peripheral T-cell lymphoma show similar findings,” Dr. Stellman said.
“A study is only as good as the data. As epidemiologists, we need to be able to measure the reliability of what we are reporting, and that has been lacking so far,” Dr. Weinstock stated. ■
Disclosure: Drs. Weinstock and Stellman reported no potential conflicts of interest.
1. Weinstock M, Stellman S: Introduction to epidemiology and population studies. 3rd World Congress of Cutaneous Lymphomas. Scientific Session D. Presented October 26, 2016.