More people are dying from melanomas thinner than a dime than from the thicker cancerous skin lesions long thought to be more dangerous, according to a new study from Queensland, Australia.

Thin tumors, which are less often lethal but far more common, accounted for almost one quarter of melanoma deaths in Queensland in the most recent period studied, compared to 14 percent of deaths blamed on thicker tumors.

More research is needed to understand which thin tumors are the most deadly, researchers say.

“We wanted to know whether the people dying from melanoma were mostly those who had ‘slipped through the net’ and were presenting to medical care with thick (advanced) melanomas,” David Whiteman, who led the study, told Reuters Health in an email. “What we found was, in fact, that many people who die from melanoma actually had thin (early) melanomas.”

Whiteman, who heads the Cancer Control Group at the QIMR Berghofer Medical Research Institute in Queensland, said melanomas tend to burrow and “invade” blood and lymph vessels, sometimes growing into secondary cancers in the brain, bones and lungs.

“The chances of secondary spread are greatly reduced by catching melanomas when they are thin, that is, before they have had a chance to “burrow” into the deeper structures of the skin,” he said.

Australia’s public health campaign to reduce skin cancer, launched in 1981, helped to lower rates of melanoma in people under 40 through prevention, the study team writes in the Journal of Investigative Dermatology. But concurrent awareness efforts have also raised the sheer numbers of tumors diagnosed, they note.

Melanoma, considered the deadliest type of skin cancer, most often affects fair-skinned people exposed to large doses of ultraviolet radiation from the sun or tanning beds. Queensland, a tropical region, has the highest rate of skin cancer in the world.

In the United States, there were 21.3 new cases of melanoma per 100,000 people from 2007 to 2011, according to the National Cancer Institute. An estimated 76,100 new cases will be diagnosed this year and 9,710 people will die from the disease.

Melanoma rates in the U.S. have doubled since 1973, a trend often attributed in large part to sunbathing and other leisure-time UV exposure (see Reuters Health story of October 8, 2014 here: reut.rs/1v6zqra).

Past research has found that patients with thin lesions (less than or equal to 1 millimeter) survived, on average, for 20 years after diagnosis, while those with thicker melanomas were more likely to die years sooner.

That’s led to a perception of thin tumors as less deadly, but Whiteman’s team writes that not enough research had looked at the distribution of deaths in the population from melanoma by tumor thickness.

They reviewed data on 4,218 Queensland residents who died from skin melanomas between 1990 and 2009, looking at age and death rates for the lesions by thickness of the first tumor diagnosed.

Thick skin tumors were defined as 4mm or more and thin tumors were 1mm or less. Thin tumors made up 68 percent of all melanomas.

Deaths from these thinner lesions nearly doubled between 1990-1994 and 2005-2009, jumping from 14 percent to 23 percent. Deaths from thick lesions remained stable at 14 percent through the study period.

People with thin lesions died about six years after they were diagnosed, while those with thick lesions died two years after the melanoma was detected, according to the data.

“This article reminds us that even though thin melanomas have an excellent prognosis, a small percentage of these tumors can still be fatal,” said Dr. Jennifer Stein, an associate professor of dermatology at NYU Langone Medical Center who was not involved in the research.

“Because thin tumors are so much more common than thick ones, they account for a disproportionate percentage of melanoma deaths,” Stein told Reuters Health in an email.

Stein pointed out that a similar study in the United States in 2010 also found that many melanoma deaths came from thin lesions.

“Just to clarify, this does not mean that thin melanomas are more fatal than thick ones,” Stein said. “It’s also a reminder that people with thin melanomas have an excellent prognosis and deaths from early melanomas are rare.”

Dr. David Polsky, a professor of dermatologic oncology at NYU Langone, said the results also showed the importance of early detection.

“This study reminds us that a small fraction of early stage cancers can and do kill patients, and this fact is responsible for many melanoma deaths,” Polsky said.

“Patients, doctors, and other health providers and payers need to remember that early detection remains the key to the greatest chance of a simple cure by surgery," he said.