Out of the 74,000 people expected to be diagnosed with melanoma this year, almost 10,000 will die, the National Cancer Institute estimates. But skin cancer doesn't grow in moles alone, researchers reported earlier this month at the American Society of Clinical Oncology annual meeting.

In fact, based on their analysis of 2,250 people with melanoma, the team found that non-mole melanomas tend to be both more common and more aggressive.

"We think that there are biological differences" between mole and non-mole melanomas, and these differences may account for the difference in aggressiveness, the lead researcher tells LiveScience.

Only between 20% and 30% of melanomas are associated with moles, they found, while the "de novo" cases—those without moles—were more than twice as likely to have cancer advanced past stage 1 when diagnosed.

Furthermore, people with de novo melanomas were twice as likely to have thick tumors and 1.6 times as likely to have broken or uneven skin than those with mole-related melanomas.

Though it's unclear why, women with de novo melanomas had higher survival rates, while men and women had roughly equal rates when the melanomas were associated with a mole.

"It's very exciting to have some new questions to investigate," the researcher said. (A favorite addiction may help reduce the risk of malignant melanoma.)

This article originally appeared on Newser: Deadly Skin Cancer Doesn't Grow in Moles Alone

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