Providence, R.I. - The incidence of cutaneous T-cell lymphoma (CTCL) has increased steadily over the last three decades, according to a new study published in the July issue of Archives of Dermatology.
This most extensive study to date also confirms significant racial and gender differences in the incidence of the disease.
Martin A. Weinstock, M.D., Ph.D., a professor of dermatology at the Brown University Warren Alpert Medical School, and medical student Vincent D. Criscione mined data from the 13 population-based cancer registries of the Surveillance, Epidemiology and End Results (SEER) Program of the National Cancer Institute for the years 1973 to 2002.
Blacks had the highest incidence of CTCL of any group: 9.0 cases per 1 million person-years. The category of "others," primarily East Asians, had an incidence rate about half that (4.9), while whites fell in between (6.1).
"The finding that rates are higher among blacks than whites cannot be explained by access to healthcare, since, in general, whites have better access to healthcare," Dr. Weinstock says. "Whether the difference would be even larger if one were to correct for access to healthcare ... we don't really know.
"It has been known for some time that CTCL is more common in men than in women; our study confirmed that," he says.
The male-to-female ratio is roughly equivalent in young adults, but it increases with age, so that in those over age 60, the rate of diagnosis in males is more than twice that in females.
Another interesting finding is that higher incidence correlates with several indicators of higher socioeconomic status of the areas - not the individuals - in the SEER data set. San Francisco had the highest rates of newly diagnosed cases (10.8 blacks; 9.7 whites), while Iowa had the lowest (5.8; 3.7, respectively).
"That suggests that having a higher social class is associated with greater incidence. That may be due to better detection and diagnosis," Dr. Weinstock says, and he notes a similar class association with incidence of melanoma.
He acknowledges that part of the increase in incidence over time might be attributed to better diagnosis, but "with three times more frequency, you would have to think that there were lots of people in the earlier periods who had it for quite a while, undiagnosed, in order for us to attribute this to diagnosis or integrity of surveillance."
Also, he notes, "One of the issues complicating figuring out what is going on with this tumor is that the classification structure has changed over time."
Identification of mycosis fungoides once clinched the diagnosis, but the classification has expanded to include other forms of T-cell lymphomas as well.
Dr. Weinstock calls CTCL "an enigmatic disorder, because we don't know the cause, we don't know why it is increasing in incidence, and we don't know why we observe these trends."
The fact that this is an indolent lymphoma further complicates tracing back to identify a causal agent, he says. The typical initial presentation as a rash is a trait shared by many disorders, while unique clinical manifestations that allow a definitive diagnosis do not appear until later in the course of disease.
A number of causal factors have been proposed over the years, but none has stood up to examination, Dr. Weinstock says.
Acute T-cell lymphoma leukemia has a similar presentation and is caused by a retrovirus, but no similar retroviral agent has been associated with CTCL.