NEW YORK, Mar 16 (Reuters Health) -- A genetic test can accurately
distinguish between melanoma and benign moles, researchers from the University
of California, San Francisco, reported recently at the annual meeting of the
International Society of Dermatopathology, held in San Francisco. While the test
is experimental and can be performed only in research labs, it may one day be
used to test moles for signs of cancer.
Currently, a suspicious-looking mole is removed and checked under a
microscope for changes indicative of cancer -- a method that does not always
provide clear results. Using traditional methods, a skilled pathologist and a
dermatologist together can correctly distinguish between the two about 95% of
the time, co-investigator Dr. Philip LeBoit told Reuters Health.
"What this test will do, hopefully, is take those cases in which there would
be some controversy and in at least the vast majority of them, give a clear-cut
answer," he said. The test, which was developed by Dr. Boris Bastian and
colleagues, is called comparative genomic hybridization and uses fluorescent
dyes of different colors to tag DNA. Most cancer cells have damaged DNA, and end
up with too much or too little genetic material in certain regions. The
different colors help identify losses and gains of chromosomal material in the
tumor DNA compared with normal DNA, LeBoit explained.
The technique "gives a very rough overview of where the gains and losses on
different chromosomes are," he said. "It turns out that in melanoma, almost all
cases have gains, losses, or both, and there's a characteristic pattern." So
far, the investigators have looked at 101 melanoma cases, and found that 82% are
missing portions of one arm of chromosome 9, 63% are missing parts of chromosome
10, and 50% have extra DNA on chromosome 7. Most human cells have 23 pairs of
DNA-containing chromosomes, for a total of 46 in each cell.
In particular, the researchers have found that one type of benign, pink
growth (known as Spitz nevi) often seen in children -- which may be mistaken for
melanoma -- has excess DNA on chromosome 11p. "Melanomas never seem to give an
amplification of the entire short arm of 11p as their only abnormality," LeBoit
said. In fact, they have only found one melanoma out of 101 with this
abnormality at all.
The researchers have only examined 16 Spitz nevi, but they believe the test
would help distinguish between the growth and cancer.
Since the technique is difficult and labor intensive to perform, he said
that they currently use it "judiciously." The best hope, LeBoit noted, is to
eventually convert the test into an easier-to-perform version that can be done
by any laboratory.
