Genetic test for melanoma developed at UCSF

By Kevin Boyd on March 09, 2000

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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