According to researchers in the U.S. recurrent melanoma is more common than previously thought, and as many as 15 percent of people diagnosed with the potentially fatal skin cancer are at risk of a second diagnosis within two years.

Melanoma begins in cells known as melanocytes, which produce the pigment that gives skin its color.

It is a particularly virulent form of skin cancer and can spread quickly and unpredictably to other organs of the body.

The researchers say that as many as 6 percent of patients will develop a second melanoma within one year of the initial diagnosis, while 8 percent will be diagnosed with a second malignancy within two years and those with atypical moles appear to be at higher risk.

The researchers from Dartmouth Medical School in Hanover, New Hampshire, say this is far more frequent than previously thought and points to the importance of surveillance and skin screenings.

Linda Titus-Ernstoff, Ph.D.,and colleagues examined the frequency of and risk factors for recurring cancer among 354 New Hampshire residents with a first diagnosis of cutaneous melanoma.

Participants completed a 40-minute telephone interview and answered questions about medical history, demographics, eye and hair color, sun exposure and whether their skin tanned, burned or freckled in the sun.

They then underwent a skin examination, during which a physician identified and catalogued benign and atypical moles.

Atypical moles have at least three of the following features: a diameter larger than 5 millimeters, redness, an irregular or ill-defined border, a variety of colors or a portion that is flat.

The study found little relationship between risk and benign moles, eye and hair color, and a lifetime history of sun exposure did not appear to influence the risk of recurring melanoma, but those with a history of sunburn were less likely to develop a second melanoma than those without.

The researchers caution against reading into this result and say those who are predisposed to develop multiple melanomas may be less susceptible to sunburn than those with one melanoma, or they may be more likely to avoid sun exposure.

They say the association should not be interpreted that sunburn protects patients with melanoma from developing additional tumors.

According to the American Cancer Society, 62,000 Americans are diagnosed with melanoma each year and nearly 8,000 people die from the disease annually.

In one-third of the patients who developed another melanoma within two years, the subsequent melanoma was deeper than the first.

The study is published in the April issue of Archives of Dermatology.