Sentinel node biopsy in melanoma

"The clinical value of sentinel lymph node biopsy in general is three- pronged," says John A. Zitelli M.D., clinical associate professor at the University of Pittsburgh Medical Center.

"First, staging is used to determine the probability of node metastasis. Staging can aid the physician in reaching decisions concerning complete node dissection, as well as in choosing an appropriate adjuvant therapy for the patient. Second, estimating a patient's prognosis can be facilitated and better evaluated, and third, patients can be stratified for on-going research."

Analyzing biopsy for melanoma

"In cutaneous oncology, the situation is slightly different," Dr. Zitelli says.

"The clinical value of SLNBx for sarcomas is shown to be negligible, and there is no evidence of any value for SLNBx in squamous cell carcinoma, Merkel cell carcinoma, sebaceous carcinoma or extra-mammary Paget's."

To determine whether the same holds true for malignant melanoma, Dr. Zitelli analyzed the results of the multicenter selective lymphadenectomy trial (MSLT-1). In the study, patients with a melanoma thickness of 1.5 mm to 3.5 mm were stratified into two groups.

The first was the observation group, where the tumors were excised and then patients were closely followed. Here, complete lymph node dissections (CLND) were done only as palpable nodes appeared.

The second was the sentinel node biopsy group, where the patients were observed if the nodes were negative and CLNDs were carried out if the nodes were positive.

Results showed that the five-year melanoma-specific survival rates were similar in the two groups (87.1 percent and 86.6 percent), and that the five-year disease-free survival was better in the sentinel node biopsy group (78.3 percent vs. 73.1 percent). Dr. Zitelli notes that a positive sentinel node was the most important prognostic factor in the biopsy group.

"With both groups randomized equally, one would expect each group to have the same survival, nodal metastasis and distant metastasis rates, unless treatment affected any outcome. Survival was the same for each group, with the same proportion of melanoma-specific deaths occurring in each group," Dr. Zitelli explains.

Questionable interpretation

Dr. Zitelli says that there was a major error in the interpretation of the results, specifically that the study compared nonmatched groups, leading to less-than-true results.

He says that in the study, 15.6 percent of the patients in the observation group had clinically significant palpable disease. The SLNBx group was expected to have 15.6 percent of patients having potential for significant disease. Here, data showed 16 percent to have a positive SLNBx, and 3.4 percent additional patients developed palpable nodes in the SLN negative group. That's a total of 19.4 percent in the SLNBx group with microscopic disease.

According to Dr. Zitelli, if the 15.6 percent who are clinically significant are subtracted from the 19.4 percent who have microscopic metastases, actually a total of 3.8 percent of patients have clinically insignificant metastases. Therefore, 24 percent (3.8/16) of +SLN patients had clinically insignificant metastases.