The test could significantly improve survival among those whose affected lymph nodes are then removed, the researchers said.
Culminating nearly two decades of international research, the study provides the first long-term evidence affirming the value of a procedure known as "sentinel node biopsy" for intermediate and thick melanoma lesions, the study authors said.
The study compared melanoma patients during a 10-year period. Among people with intermediate-thickness lesions, those whose lymph nodes were removed after their sentinel node biopsy tested positive for cancer were 44% more likely to survive their melanoma, said study author Dr Mark Faries.
The other "watchful waiting" group of patients didn't have their nodes removed until the disease was later found to have spread." It makes sense: Those who were not treated up front had their melanoma spread from the sentinel lymph node to other lymph nodes in the area, [which can facilitate] a spread throughout the body," Faries said. "This study provides concrete evidence that everything we had assumed about the sentinel node procedure ... and lymph node treatment is true."
Risk factors for the disease
According to the American Cancer Society, lymph nodes are small structures that work as filters for harmful substances in the body. They contain immune cells that can help fight infection by attacking and destroying germs in lymph fluid.
The study by Faries, director of melanoma research at the John Wayne Cancer Institute in Santa Monica, California., and colleagues was published online in the New England Journal of Medicine.
Melanoma is diagnosed in about 120 000 Americans each year and kills about 9 000 annually, according to the Skin Cancer Foundation. The strongest risk factor for the disease is intense, periodic exposure to ultraviolet light from sunshine or tanning beds, but other risk factors include fair skin and family history.
Initiated in 1994, the study randomly assigned about 2 000 patients with melanoma to two groups. The observation group had their lesion removed and their lymph nodes observed for recurrence, at which time they were removed. The biopsy group underwent lesion removal and a sentinel node biopsy, with immediate lymph node removal for patients whose cancer had spread to the sentinel node.
In melanoma, a sentinel node biopsy removes the lymph node nearest a lesion and tests it for evidence of cancer. If the sentinel node is unaffected, the cancer is highly unlikely to have spread to surrounding lymph nodes or distant sites in the body. The biopsy procedure is also used in other malignancies, particularly breast cancer.
In the new study's biopsy group, sentinel node results were the most important predictor for 10-year survival of melanoma among patients with lesions considered intermediate or thick.
Disease-free survival rates over 10 years were significantly better in the biopsy group among patients with intermediate melanoma (about 71% compared with 65%) and thick melanoma (nearly 51% versus about 41%).
Among patients whose cancer spread to the lymph nodes from an intermediate-thickness melanoma, biopsy yielded better 10-year disease-free survival to distant organs as well as better overall survival from melanoma.
Removing all lymph nodes from an area of the body can trigger painful, chronic tissue swelling known as lymphedema. But this risk for melanoma patients can be supported by the survival-rate improvements documented in the new study, said Dr Charles Balch, a professor of surgery in the division of surgical oncology at University of Texas South-western Medical Centre, in Dallas.
Balch, who co-wrote a journal editorial accompanying the study, called the research "practice-changing" because of the length of the clinical trial and the strength of the findings.
"If we know there's an increase for leg or arm swelling, we can justify [node removal] more to the patient if it increases survival," Balch said. "This is the largest study ever done on this subject, and it's multinational with the longest follow-up. It's really a seminal work."