Comparison Examines GEP Performance Against Melanoma SLNB Risk Thresholds
Key Takeaways
- A comparison of two prospective melanoma studies found differences in the ability of gene expression profiling (GEP) assays combined with clinicopathologic factors to identify patients with a less than 5% risk of sentinel lymph node (SLN) positivity.
- In the DECIDE study, patients with an i31-SLNB predicted risk below 5% had an observed SLN positivity rate of 2.6%, compared with 7.1% among patients classified as low risk by 10-GEP+CP in MERLIN_001.
- The findings come from separate study populations rather than a head-to-head trial, limiting direct comparisons of test performance and clinical utility.
A comparison of two prospective studies evaluating gene expression profiling (GEP) tests combined with clinicopathologic factors found differences in their ability to identify patients with cutaneous melanoma at low risk for sentinel lymph node (SLN) positivity.1
The poster, presented at the 2026 Fall Clinical Dermatology Conference, compared findings from the DECIDE study, which evaluated the integrated 31-GEP test (i31-SLNB), and MERLIN_001, which investigated the 10-GEP+CP assay. Both studies assessed whether molecular testing could identify patients eligible for sentinel lymph node biopsy (SLNB) whose actual nodal positivity risk was below 5%.
Differences in SLN Positivity Across Melanoma Risk Groups
According to the analysis, patients with an i31-SLNB predicted risk below 5% had an observed SLN positivity rate of 2.6%, compared with 7.1% among patients classified as low risk by 10-GEP+CP.
In patients with T1b-T2a melanoma, SLN positivity was 1.4% in the i31-SLNB group with predicted risk below 5%, compared with 6.5% in the 10-GEP+CP low-risk group.
The investigators reported that MERLIN_001 did not meet its primary endpoint of identifying SLNB-eligible patients with less than 5% SLN positivity risk. In contrast, DECIDE identified a subgroup with observed positivity below that threshold.
The analysis referenced National Comprehensive Cancer Network guidance, which uses SLN positivity risk thresholds to inform SLNB discussions.
However, the comparison was based on results from two separate prospective studies rather than direct testing of both assays in the same population. Differences in study populations, assay outputs, and methodology limit comparative conclusions.
The poster was authored by J. Michael Guenther, MD; Andrew Lewis, PhD; and Peter A. Prieto, MD. They concluded that i31-SLNB identified patients with observed nodal positivity below 5%, whereas the 10-GEP+CP low-risk classification did not achieve that threshold in MERLIN_001.
1. Guenther JM, Lewis A, Prieto PA. Tale of Two Prospective Studies Using Different CP+GEP Tools to Predict SLNB Positivity in Melanoma: Differential Outcomes and NCCN Opinions. Research poster supplied for editorial review.