The Journal of the American Medical Association Dermatology recently published their study on its online site.

"First, we wanted to know if people with a single primary tumor were more likely to die from melanoma than people with multiple primary tumors," says Dr. Berwick. "They're not. But, if you match the thickness of the tumor, people with multiple primary tumors survive better." Dr. Berwick is a University of New Mexico Distinguished Professor of Epidemiology at the UNM Cancer Center.

The team included researchers in Australia, Italy, Canada and elsewhere in the United States. For this study, they asked 3,578 participants, newly-diagnosed with skin cancer, to answer a lengthy set of questions about their personal history, family history and lifestyle. The team also fully analyzed tissue and DNA samples from each person to obtain information about how many tumors and what mutations each person had, how thick the tumors were, how actively each tumor was growing, and whether or not the tumor surface had broken. Because of the large number of people, Dr. Berwick and her team could draw meaningful relationships between tumor qualities and people's health.

"Usually, we try to match a person who's just been diagnosed with a healthy person from the general population," says Dr. Berwick. "But that's impossible to do anymore." She explains that to find healthy people to participate in a study, researchers used to randomly dial phone numbers. "Do you answer the phone?" Dr. Berwick asks with a sly grin. So, the researchers chose instead to look at how different aspects of skin cancer affect survival and made some compelling discoveries.

The team evaluated several different factors, including the age and sex of the person, where the skin cancer was on the body, and whether they had only one tumor or more than one tumor when initially diagnosed. Most of the factors weren't statistically significant. But if the tumor created an ulcer in the inner layer of skin, called the dermis, or if the tissue sample analysis showed that the tumor was rapidly growing, surviving melanoma was a little less likely. The most significant factor was tumor thickness. People whose tumors had grown 4 millimeters or more into the dermis, were 7.7 times more likely to die than someone whose tumor had penetrated only 1 millimeter into their dermis.

The research team then compared tumor thickness with the number of tumors at initial diagnosis. They got a surprise. They found that for people with multiple primary tumors, those whose tumors were 4 millimeters or deeper were almost three times more likely to die than those whose tumors were only 1 millimeter. But for people who had a single primary tumor, those whose tumor was 4 millimeters or deeper were 13.6 times more likely to die than those whose single tumor was only 1 millimeter. "Many people would think the opposite," says Dr. Berwick, "because they think having more tumors is worse. It seems that those people with multiple melanoma have some sort of native immune factor that's helping them. It's keeping the melanoma in check."

To learn more about why people with single primary tumors die at a much higher rate, Dr. Berwick and her international team are planning more studies to search for important immune biomarkers and to analyze how sun exposure affects skin cancer survival, an area in which Dr. Berwick is particularly interested. They will also examine tumors in more detail. "You can't tell by looking [at a tumor] how thick it is," she says. Dr. Berwick strongly recommends visiting a dermatologist if a blemish looks amiss or if a mole is growing.

"It's very exciting work," she explains enthusiastically, "because there has been no cure for people who have deep melanomas. We're just at that point where we can start to make a difference and that's very motivating."