Mar. 13, 2000 San Francisco - A genetic test to help pathologists identify melanoma, the most common type of skin cancer, has been developed by researchers at University of California, San Francisco, and may be available to pathology labs within a year.
The test, which detects chromosomal abnormalities that characterize cancerous skin cells, was described here, today (March 9), at the annual meeting of the International Society of Dermatopathology.
A skin mole that looks suspicious to a dermatologist is usually biopsied and examined under the microscope. But even with years of experience it's sometimes impossible to make a clear decision as to whether or not the mole is cancerous. And sadly, many melanoma cases slip through the screening process; according to some insurance carriers, these cases account for six percent of the money awarded each year in malpractice suits.
Because melanoma results when a cell's genetic machinery gets out of control, Philip LeBoit, MD, a professor of pathology at UCSF, and his colleagues began comparing chromosomes of normal skin cells with those of cancerous ones. In a test called comparative genomic hybridization, they labeled DNA from normal and cancerous cells with different fluorescent dyes, then used these to identify the changes in the cancer cell's chromosomes.
These experiments were conducted by Boris Bastian, MD, an assistant professor of dermatology, Dan Pinkel, PhD, a professor at the NCI-designated UCSF Comprehensive Cancer Center, and LeBoit.
Clear patterns have emerged in the first 100 cases that LeBoit and his colleagues have studied: 82 percent of melanoma tumors lack portions of the DNA normally found on one arm of chromosome 9, 63 percent are missing sections of chromosome 10, and 50 percent of tumors have extra DNA on chromosome 7. Cancer cells that are missing DNA have shut down certain genes on that chromosome and, similarly, extra DNA suggests that the melanoma has generated extra copies of some genes on that chromosome.
By testing suspicious looking skin cells for these abnormalities, dermatologists can be much more certain of their diagnoses, LeBoit said. "Now we have a common set of abnormalities for melanoma. And most tumors have two, three or four of them," he said.
Before pathology labs around the country can begin using the test, it needs to be simplified, LeBoit said. "It now takes a more sophisticated molecular biology lab and weeks to months of work to get an answer for a given case," he said. The experimental version of the test will be replaced by one that uses fluorescent markers to light up the aberrant chromosomal regions in tumor cells. "This type of fluorescent test is much easier to do technically," he said.
The chromosomal tests should also help when a melanoma is discovered, by showing where the cancer stops and the normal cells begin. This will enable dermatologists to cut out only the cancerous cells and leave behind the healthy ones, LeBoit said.
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