HealthyCanada.com

2003/2/7

Now researchers from Harvard's Dana-Farber Cancer Institute say they may finally know why.

In a study that appears in this week's Proceedings of the National Academy of Sciences the researchers used newborn mice to illustrate how the sun's rays damage something called the Rb pathway -- a chain of biochemical signals that regulate cell activity including suppressing the growth of malignant tumor cells.

"I think the key finding of our study is the observation of Rb pathway being hit specifically by UV [ultraviolet rays] and the potential implication of this" says study author Dr. Lynda Chin an assistant professor of dermatology at Harvard Medical School.

Essentially a tumor develops when normal cells experience environmental or other types of damage causing them to reproduce at an alarming rate. Under normal conditions Chin says the Rb pathway will sense something is not right within the cell and turn off its ability to clone itself. This in turn stops tumor formation.

However if the Rb pathway becomes damaged by UV rays particularly before the age of 17 researchers say the pathway's tumor-suppressing powers are compromised. With each new environmental assault including sun exposure the chances of malignant cells developing increases.

What's more Chin says damage to the Rb pathway appears to be a direct link to melanoma the deadliest form of skin cancer.

"Rb pathway is presumably constraining growth of to-be melanoma cells; the UV inactivates this [protection] to allow melanoma to develop" Chin explains.

If not treated early melanoma is among the most aggressive cancers and rapidly spreads to cells throughout the body. According to the Canadian Cancer Society the incidence of skin cancer has risen from 40000 cases in 1989 to 70000 in 2001 including 3800 melanomas. However if caught early those damaged cells can be surgically removed halting the spread of disease and dramatically decreasing the risk of death experts say.

For dermatologist Dr. Ted Daly the new research represents a departure from the way in which doctors previously viewed the sun's role in skin cancer.

"The accepted dogma was that the solar radiation hits a gene spot and causes kind of like a break in a zipper so the cell no longer can divide correctly" says Daly director of Pediatric Dermatology at Nassau University Medical Center. The new theory points up an entirely different path of destruction that while hopeful remains to be proven in humans he adds.

"The negative is that mice are not men so there's still a long way to go" Daly says.