Updated 21 August 2014

Deadliest melanomas usually found on head and neck

Researchers have found that the most dangerous skin cancers usually occur on the head and neck of older men and are colourless, making them harder to detect.

The speed at which cancer cells grow may help doctors diagnose and treat the most aggressive melanomas, researchers say.

Using this measure, investigators have found that the deadliest skin cancers occur most often on the head and neck of older men with a long history of sun exposure.

High mitotic rate

These lesions also grow quickly and are often colourless, the researchers discovered.

Rapid cell growth, called high mitotic rate, is associated with poorer prognosis in patients with melanoma. For this new study, the Australian research team examined the physical characteristics of melanomas and their rate of cell division to help doctors know how to spot these faster-growing cancers.

Are you at risk of melanoma

Currently, the seriousness of a melanoma is established by its depth. "Now we might add the mitotic rate as part of that prognostic factor," said Dr. Doris Day, a dermatologist at Lenox Hill Hospital in New York City, who had no part in the study.

"You would expect that cells that are dividing faster make for more aggressive melanomas that are going to have a worse prognosis," said Day.

That most of these aggressive cancers were found on exposed areas of men with significant sun histories indicates that prolonged exposure to sunlight increases the odds of having more aggressive melanomas, Day noted.

"It makes me worry about all these young women who go to tanning salons, because of their chronic exposure," Day said. "I'm worried that 20 or 30 years from now we are going to see these women developing this worse type of melanoma."

In the United States, about 9,000 people die of melanomas of the skin each year, according to the U.S. Centres for Disease Control and Prevention.

Men most at risk of melanoma

Diagnosing and treating melanoma

Day said the key to treating melanoma is diagnosing it early.

Perhaps melanomas with high mitotic rates will be treated differently than those with lower rates, she added.

"We may now get more aggressive in the treatment of melanoma that is not deep but has a high mitotic rate. Instead of just cutting it out, we may add in chemotherapy," she said. "So we may change how we evaluate melanomas and how we treat them."

But before mitotic rate can be used as a predictor of the aggressiveness of melanomas, the results from this study will have to be duplicated, Day said.

Another expert, Dr. Homere Al Moutran, of Staten Island University Hospital in New York City, agreed. "Mitotic rate, even though not universally evaluated for melanoma, has been shown to be a significant prognostic indicator in skin cancer," he said.

History of sun damage

The American Academy of Dermatology says inclusion of mitotic rate in skin cancer reports is an option, he noted. "This study shows a possible particular behaviour for mitotically active melanoma, but more studies are needed to define whether mitotic rates should become a standard independent factor in these tumours," Al Moutran said.

For the study published online in JAMA Dermatology, a research team led by Dr. Sarah Shen, from Alfred Hospital in Victoria, looked at the mitotic rates of melanomas in more than 1,400 patients.

The investigators found that melanomas with higher mitotic rates were more likely to occur on the head and neck, grow faster and appear without colour.

These cancers were more likely to occur in men 70 and older and in people with a history of sun damage. Called solar keratosis, these are rough, raised areas on skin that have been exposed to the sun for long periods.

A history of blistering sunburns and a family history of melanoma, however, were associated with cancers having lower mitotic rates, the researchers said.

New treatments in the pipeline

New treatments are improving survival of people with advanced melanoma, Day said. "There are now some genetic-based treatments and some immune-based treatments," she said.

"This has taken what was a death sentence and made it into a chronic illness. People are now living four and five years when they would have died in six months," Day explained.

What's sad, she added, is that skin cancer is largely preventable. "A lot of cancers you can't do anything about, but skin cancers are up to 80 percent preventable by just adjusting behaviour," she said.

Read more:

Experimental melanoma drug shows promise

Women more likely to survive melanoma
Melanoma rates on the rise

Image: Senior man walking in the park in autumn from Shutterstock

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