"For patients with melanoma, survival beyond 10 years without a recurrence has been considered nearly synonymous with a cure," said principal investigator Mark Faries, MD, FACS, a professor of surgery at the John Wayne Cancer Institute at Saint John's Health Center, Santa Monica, CA. "However, most studies do not follow up patients longer than 10 years. Our study found that late melanoma recurrence is not rare and that it occurs more frequently in certain patient groups."

Patients with a higher chance of melanoma -- the deadliest form of skin cancer -- recurring more than a decade later, compared with early recurrence of melanoma within the first three years, were typically a younger age at initial diagnosis and generally exhibited less serious characteristics of the original tumor, Dr. Faries and colleagues reported.

Dr. Faries said the study represents the largest reported group of melanoma patients with a first recurrence at least a decade later. Of 4,731 patients who were diagnosed with skin melanoma at their medical center and received long-term follow-up, 408 patients experienced a late melanoma recurrence after being disease free 10 or more years, the authors reported.

Recurrence rates using actuarial analysis were reportedly 6.8 percent 15 years after initial treatment and 11.3 percent at 25 years.

When the investigators determined the melanoma recurrence rate by including only patients who received initial treatment at the John Wayne Cancer Institute, they found that 327(6.9 percent) of the 4,731 patients showed a late recurrence.

"It appears the risk of melanoma recurrence is never completely gone," Dr. Faries said. "One change that should result from our study is that people need to be followed up for life with a physician after a diagnosis of melanoma." The American Cancer Society estimates that nearly 76,700 new cases of melanoma will be diagnosed in the U.S. this year according to 2013 estimates, with more men affected than women.

The new study findings, however, showed that late melanoma recurrence was less male-predominant than in patients whose cancer recurred within the first three years. Although 66 percent of 3,127 patients with an early melanoma recurrence were men, only 57 percent of the 408 patients with a late recurrence were male, the investigators reported. This difference may be because initially "melanoma behaves worse in men than in women, although no one knows why," he said.

The researchers note other differences existed between patient groups. Namely, patients whose melanoma did not come back until at least 10 years later were younger, on average, than those with an early recurrence: 41 versus 51 years old.

In addition, compared with the early-recurrence group, patients with a late recurrence tended to have had an original melanoma with characteristics indicating a more favorable disease outcome. Specifically, their original tumor was more likely to have been thin and nonulcerated (meaning that the skin over the melanoma had not broken down), not have spread to the lymph nodes, and occurred at a site other than the head and neck.

Although the investigators found that late-recurring melanomas were more likely to develop in a site on the body distant from the original site, this group of patients had a better post-recurrence survival rate. Compared with patients whose cancer returned within three years, patients with a late recurrence were about 40 percent less likely to die of melanoma than were patients with an early recurrence, Dr. Faries said. Overall survival also was better in the late-recurrence group according to the researchers.

"Fortunately, the vast majority of melanoma patients who remain disease free longer than 10 years will not have a recurrence," Dr. Faries said. "However, patients should be aware that persistent or unexplained symptoms anywhere in the body might indicate a recurrence of their melanoma, and they should return to their physician to make sure the symptoms are not related."

Even when symptoms are absent, Dr. Faries recommended that patients get an annual clinical examination with their melanoma physician or primary care physician. He also orders a yearly chest X ray and laboratory tests for his melanoma patients.

Other study authors, all from the John Wayne Cancer Institute, included Shawn Steen, MD; Xing Ye; Myung Sim, DrPH; and Donald L. Morton, MD, FACS.

Study researchers received partial support from the National Cancer Institute, Melanoma Research Alliance, Dr. Miriam and Sheldon G. Adelson Medical Research Foundation, and Alan and Brenda Borstein.