There has been a steady increase in cancers of the sweat glands and hair follicles -- cutaneous appendageal carcinomas -- since the late 1970s, although the incidence of the tumors remains low, researchers found.
From 1978 through 2005, the rate of the cancers rose from 2.0 per 1 million person-years to 5.0, a 150% jump, Jorge Toro, MD, of the National Cancer Institute (NCI) in Bethesda, Md., and colleagues reported in the June issue of Archives of Dermatology.
The findings, which were originally reported at the International Congress of Dermatology last year, indicated an especially large increase in sebaceous carcinoma, from 0.6 per 1 million person-years to 1.9, a 217% rise.
The overall increase is "perhaps related to improved recognition and classification, but factors such as UV exposure and immunosuppression may also play a role," the researchers wrote.
Although the epidemiological patterns of sebaceous carcinoma have been reported, little had been known about the patterns of the other types of cutaneous appendageal carcinomas.
So Toro and his colleagues analyzed data from the NCI's Surveillance, Epidemiology, and End Results (SEER) program.
From 2001 to 2005, 1,801 patients were diagnosed with a cutaneous appendageal carcinoma. The incidence rate was 5.1 per 1 million person-years.
The most common type of cutaneous appendageal carcinoma was apocrine-eccrine, accounting for 51% of cases. Sebaceous tumors occurred in 35% of cases.
Cutaneous appendageal carcinomas overall and sebaceous carcinomas, in particular, occurred disproportionately on the face, scalp, and neck, with those sites involved in more than 63% of cases.
Most apocrine-eccrine carcinomas were also on the face, scalp, and neck (55%), but there were some variations by subtype.
Men had a significantly higher rate than women (6.3 per 1 million person-years versus 4.2, P<0.001).
The cancers also occurred at a significantly higher rate among non-Hispanic whites (5.7 per 1 million person-years) than among Hispanic whites (3.7), blacks (3.5), and Asian/Pacific Islanders (2.5) (P<0.001 for non-Hispanic whites versus the rest).
The racial disparity was consistent across most tumor subtypes.
In line with previous observations, the rate of cutaneous appendageal carcinomas rose exponentially with age, from 0.37 per 1 million person-years for individuals in their 20s to 37.3 for those 80 and older.
Data from 1992 through 2004 were used for the survival analysis, which revealed an overall five-year survival rate of 96.5%.
Survival was greatest with localized involvement (99%), followed by regional involvement (93%) and distant involvement (43%).
Toro and his colleagues offered some possible explanations for the increase in the rate of these cancers over the past three decades, including exposure to UV radiation. The racial differences identified in the study are consistent with this hypothesis, they said.
The immune system may also be a factor since the risk of developing cutaneous appendageal carcinomas is greater among immunosuppressed individuals. The authors wrote that the increase in these lesions tracked an "... increasing population of immunosuppressed individuals due to infection (i.e., HIV), immunosuppressant drugs for organ transplant, and/or rheumatologic or other inflammatory diseases."
The researchers noted some limitations of the analysis, including the lack of statistical power for some analyses because of the small number of cases and the lack of a centralized pathologic review of cases.
In addition, they wrote, error could have been introduced through missing or incomplete data in the SEER registries, and rates of disease could have been underestimated because of reporting delays or incomplete inclusion of all patients in the registries.
Primary source: Archives of Dermatology
Source reference: Blake P, et al "Cutaneous appendageal carcinoma incidence and survival patterns in the United States: a population-based study" Arch Dermatol 2010; 146: 625-32.