A new Hutch study suggests that more cases of non-invasive melanoma, a form of skin cancer, may be slower-growing than previously suspected.
The findings could have practical implications for cancer screening and may also provide a better perspective on the aggressiveness of these tumors.
But the findings do not mean that potential cases of skin cancer should be taken lightly, said Dr. John Lee, an investigator in the Public Health Sciences Division and the author of the study.
"Nothing needs to change in terms of the public-health message," he said, "but this may give us some insight into the mechanisms that control whether or not a tumor becomes invasive."
The study appears in the October issue of Melanoma Research.
Melanoma is the most serious form of skin cancer and affects pigment-producing cells known as melanocytes.
Although melanoma accounts for only 4 percent of all skin cancers, it causes almost 80 percent of all skin-cancer deaths. This year, more than 50,000 cases of melanoma will be diagnosed, and about 7,800 people will die of the disease.
Lee studied incidence of invasive and in situ (localized to the outer layer of the skin) melanoma in white populations from 1975 to 1997. Information for the study was obtained from the Surveillance, Epidemiology and End Results (SEER) Program, a network of regional population-based cancer registries supported by the National Cancer Institute.
Although the incidence of both types of melanoma has increased during the time period studied, incidence rates of the localized form have increased more rapidly than those for invasive melanoma.
In his analysis of the data by age group, Lee observed that patients with in situ tumors were older than those with invasive tumors
"For example, in both men and women aged about 35, those with in situ tumors were about 2.7 years older than those with invasive," he said.
Because sun damage to the skin early in life is a risk factor for skin cancer, these findings suggest that the localized tumors in older populations are slow-growing.
While public awareness of skin cancer has increased in recent years, Lee said that changes in cancer screening behavior alone cannot account for the more rapid increase in localized cases of cancer.
Of interest, he said, would be more direct analysis of the tumors themselves.
"Future research might reveal the control factors that cause some tumors to sit there for many years doing nothing while others - the more aggressive ones - kill people."