Less than one-third of melanomas (29 percent) arose from an existing mole, while the vast majority (71 percent) appeared on the skin as new spots, according to research in the Journal of the American Academy of Dermatology.

Moreover, melanomas that arose from existing moles were thinner than other melanomas, indicating that patients whose melanoma was associated with an established mole had a better prognosis than others.

To arrive at their findings, researchers reviewed 38 published studies comprising 20,126 melanomas.

“These results could indicate that patients who monitor their existing moles for suspicious changes could detect melanoma in its early stages, when it’s most treatable,” says study author Caterina Longo, MD, PhD, a dermatologist at the University of Modena and Reggio Emilia in Italy, in a news release. “Because the disease is more likely to appear as a new growth, however, it’s important for everyone to familiarize themselves with all the moles on their skin and look for not only changes to those moles, but also any new spots that may appear.”