Dr. James W. Jakub
Dr. Svetomir N. Markovic
Question: In which patients with melanoma should a sentinel lymph node biopsy (SLNB) be pursued?
Answer: We recommend a SLNB for patients with a negative clinical nodal exam and a life expectancy of at least 3 years who meet the following criteria:
- Melanoma greater than 1 mm in Breslow’s thickness, or
- Melanoma between 0.76 mm and 1.0 mm in Breslow’s thickness and another high-risk feature, such as young age, any mitosis, or ulceration.
In cases of transection of the base as a sole risk factor for thin melanomas, a discussion with the pathologist and clinical correlation is required. In most cases, the bulk of the gross lesion had been removed, and there is only a small focus of melanoma at the deep biopsy margin. In this situation, we would not recommend SLNB. If the biopsy was a sampling of a larger lesion or the lesion was clearly transected at the base across a deeper lesion, we would consider SLNB. A risks/benefit discussion of SLNB should be held with all patients as part of the shared decision-making process.
At the minimum, SLNB is the most reliable staging procedure for a patient who has clinically asymptomatic, node-negative disease, and the status of the regional nodal basin remains the single most significant prognostic factor. Unlike systemic imaging, which has a yield of less than 5%,1-3 SLNB identifies microscopic nodal disease in approximately 20% of patients with intermediate-thickness primaries.4 Patients with intermediate-thickness melanoma are a heterogeneous group, consisting of both patients who have microscopically positive and microscopically node-negative disease. Accurately stratifying these patients as stage I/II or stage III has implications in disease management, including the use and type of adjuvant therapy and clinical trial eligibility.
SLNB has been shown to improve disease-free survival (DFS) but not melanoma-specific survival (MSS). Eighty percent of patients with intermediate-thickness melanoma have sentinel lymph node–negative disease and cannot receive a therapeutic benefit from the procedure. This dilutes our ability to show an MSS benefit of removing microscopic disease, and no trial will be powered to overcome this. Thus, it is not expected that SLNB will improve MSS for the entire group of patients with clinically node-negative disease; however, for the 20% who have microscopic nodal disease, removing this disease with a SLNB will improve both DFS and MSS. As shown in the MSLT-I trial, essentially all micrometastases become clinically significant with time.4 Even with aggressive follow-up, the nodal disease burden in patients randomly selected to receive SLNB was, on average, one microscopically positive lymph node as compared to macroscopic disease in three lymph nodes in those randomly assigned to no SLNB.5 The absolute improvement in 10-year MSS for the cohort of patients with node-positive disease was 15% better for those randomly selected to receive SLNB compared with observation. Clinically occult disease, if observed, will likely present itself as macroscopic disease with a worse outcome. Unfortunately, without surgical and pathologic staging, vis-à-vis SLNB, we currently do not have a reliable method of discriminating preoperatively those with and those without micrometastatic nodal involvement. Ongoing research into molecular variables of the primary tumor show promise and will likely change this in the future.6 Until then, clinical staging is not reliable, and SLNB is a procedure that offers significant prognostic information and an improvement in MSS for a select group of patients who have microscopically node-positive disease. It also allows consideration of adjuvant therapy options and clinical trial participation for those with stage III disease.