However, the research, which was published in the Journal of the American College of Surgeons, found that these patients tend to live longer after their melanoma returns than patients whose cancer recurs in the first three years.
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, said:
"For patients with melanoma, survival beyond 10 years without a recurrence has been considered nearly synonymous with a cure. 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 an increased risk of melanoma (the deadliest form of skin cancer) recurring over 10 years later, compared to an early recurrence of melanoma within the first 3 years, were normally of a younger age at initial diagnosis and generally exhibited less severe characteristics of the original tumor, according to the scientists.
This investigation represents the largest reported group of melanoma patients with a first recurrence at least 10 years later, Dr. Faries pointed out.
A total of 4,731 patients, who were diagnosed with melanoma at their medical center and received long-term follow up, were involved in the study.
After being cancer-free for at least one decade, 408 of those subjects experienced a late melanoma recurrence.
"Recurrence rates using actuarial analysis were reportedly 6.8 percent 15 years after initial treatment and 11.3 percent at 25 years," the authors said.
By including only patients who received initial treatment at the John Wayne Cancer Institute to determine the melanoma recurrence rate, the researchers found that 6.9% (327) of the 4,731 patients showed a late recurrence.
"It appears the risk of melanoma recurrence is never completely gone," explained Dr. Faries. "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."
Almost 76,700 new cases of melanoma will be diagnosed in the U.S. in 2013, according to the American Cancer Society, with more males affected than females.
The new results, however, demonstrated that "late melanoma recurrence was less male-predominant than in patients whose cancer recurred within the first three years."
Males made up 66% of the 3,127 patients who experienced an early melanoma recurrence. However, only 57% of the 408 patients with a late recurrence were men.
According to Dr. Faries, this difference could be because at first "melanoma behaves worse in men than in women, although no one knows why."
Other differences were seen between patients groups. For example, patients whose cancer did not come back until at least a decade later were younger, on average, compared to those with an early recurrence (41 vs. 51 years old).
The individuals with a late recurrence were inclined to have had an original melanoma with characteristics pointing to a more favorable disease outcome, compared with the early-recurrence group.
This meant that their original tumor was more likely to have been thin and nonulcerated - the skin over the melanoma had not broken down. It was also more likely to not have spread to the lymph nodes and occurred at a site other than the head and neck.
However, "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," the results showed.
Patients with a late recurrence had an approximately 40% reduced risk of dying from melanoma compared to patients with an early recurrence, Dr. Faries said. The late-recurrence group also had better overall survival rates.
Dr. Faries said:
"Fortunately, the vast majority of melanoma patients who remain disease free longer than 10 years will not have a recurrence. 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."
Patients should get a clinical examination each year with their melanoma physician or primary care doctor, even if no symptoms are present, Dr. Faries said, who also orders an annual chest X ray and laboratory tests for his melanoma patients.
A previous study suggested that higher levels of a protein called S-100 in patients with melanoma may correlate with an increased risk of the disease returning.
Written by Sarah Glynn