GENE FOUND FOR MOST COMMON CANCER - MILD SKIN TUMORS.

Byline: Robert S. Boyd Knight-Ridder Tribune News Wire

A gene responsible for the most common type of cancer in humans has been found, two teams of scientists reported Thursday.

When the gene is damaged by ultraviolet radiation from the sun, it can produce skin tumors, known as basal cell carcinomas, that afflict about 750,000 people in the United States each year.

Pale-skinned, middle-aged and older persons of Northern European ancestry are the most susceptible to these relatively harmless growths. If caught in time, they are easily removed with minor surgery or radiation.

The discovery of the new gene could lead to the development of a less-invasive treatment by a drug or ointment applied directly to the skin, scientists said.

Unlike most other cancers, basal cell carcinomas do not migrate throughout the body. By revealing why basal cells are unable to colonize other organs, the new findings could provide clues to prevent the spread of other, more dangerous cancers of the colon and breast.

Dr. Ervin Epstein Jr., a dermatology professor at the University of California, San Francisco, added, ``This finding is exciting because for the first time we have a fundamental understanding of how this common cancer occurs and some possibility for a new treatment.''

Epstein belongs to a group of scientists, based in California and London, who reported their findings in the journal Science. Simultaneously, a rival team consisting of Australian, Swedish and American scientists published a similar report in the journal Cell.

Both groups were seeking the source of a rare - but virulent - related disease known as basal cell nevus syndrome, which mostly affects children who have been exposed to the sun. Also known as Gorlin syndrome, its symptoms include cysts in the jaw, extra fingers and abnormal ribs and vertebrae, as well as hundreds of skin tumors.

From previous studies of fruit flies, a favorite model organism for biological research, scientists knew that a gene called ``patched'' helps to control the growth of cells in flies. When ``patched'' is missing or defective, flies develop faulty wings or other abnormalities.

The research teams found an almost identical human gene on chromosome 9, one of the 23 pairs of chromosomes that carry DNA, the genetic code of life, in every cell.

Analysis showed flaws in the ``patched'' genes of persons with the nevus syndrome and basal cell carcinoma, indicating that this defect is connected with both diseases.

``Normally, cells carry two copies of the patched gene,'' said Ronald Johnson, a biologist at Stanford Medical School and a collaborator on the Science paper. ``Basal cell carcinomas usually arise when both copies of these gene are damaged by sunlight. Typically, these tumors develop fairly late in life because on average it takes a lot of sunlight to inactivate both copies of the gene in any one cell.''