Prospective Data Support i31-SLNB Test to Guide Biopsy Use in Melanoma

New prospective multicenter data suggest that the integrated 31-gene expression profile–based sentinel lymph node biopsy risk model, i31-SLNB, may help identify patients with cutaneous melanoma who are unlikely to benefit from sentinel lymph node biopsy (SLNB), according to findings presented at the 2026 Society of Surgical Oncology Annual Meeting and published in Future Oncology.¹

In the study, patients predicted by the i31-SLNB test to have less than a 5% risk of sentinel lymph node (SLN) positivity had an observed nodal positivity rate of 2.6%, consistent with the threshold recommended in the NCCN cutaneous melanoma guidelines for considering omission of SLNB. The findings come from the largest prospective multicenter evaluation to date of the integrated risk model embedded within the DecisionDx-Melanoma genomic assay.

“This study of DecisionDx-Melanoma’s i31-SLNB result confirms that the test delivers clear and clinically meaningful separation between low- and high-risk patients in real-world practice,” Timothy Beard, MD, FACS, lead author and surgeon at Summit Medical Group in Bend, Oregon, stated in a news release. “Importantly, patients identified as low risk not only had very low rates of nodal positivity but also demonstrated high recurrence-free survival over [3] years. That level of prospective validation can give clinicians and patients greater confidence when deciding whether to proceed with or forgo sentinel lymph node biopsy.”

The prospective analysis enrolled 912 patients with T1 to T4 cutaneous melanoma across 30 US centers. Among these patients, 430 underwent SLNB and 482 did not, indicating both nodal positivity rates and recurrence outcomes. The i31-SLNB algorithm integrates the 31-gene expression profile (31-GEP) score generated by the DecisionDx-Melanoma assay with clinicopathologic variables such as Breslow thickness, ulceration status, mitotic rate, and patient age to estimate an individualized likelihood of SLN metastasis.

Among patients who underwent SLNB, the test demonstrated substantial separation between predicted low- and high-risk groups. Patients categorized as having less than 5% predicted risk of SLN positivity had an actual nodal positivity rate of 2.6%. By contrast, patients with greater than 10% predicted risk had an observed positivity rate of 21.4%.

Investigators reported particularly notable risk stratification within the T1b to T2a subgroup, a population in which SLNB decisions can be clinically uncertain. Among patients in this subgroup with a predicted risk below 5%, only 1 of 74 patients (1.4%) had a positive sentinel lymph node. In comparison, patients with a predicted risk greater than 10% had an SLN positivity rate of 18.5%. According to the investigators, this corresponds to a 13.2-fold higher likelihood of nodal positivity in the high-risk group.

Outcomes analyses also suggested favorable prognosis among patients categorized as low risk by the integrated model. Individuals with an i31-SLNB predicted risk below 5% demonstrated a 3-year recurrence-free survival (RFS) rate of 97.8%, indicating a low likelihood of disease recurrence in this population.

SLNB remains an important staging tool in melanoma, but the procedure carries surgical risks and may not be necessary for all patients. Current guidelines from the NCCN recommend avoiding SLNB when the likelihood of a positive node is less than 5%, considering the procedure when the risk falls between 5% and 10%, and offering it when the predicted likelihood exceeds 10%.²

Traditional risk assessment relies primarily on clinicopathologic features incorporated into the American Joint Committee on Cancer staging system, including tumor thickness, ulceration, and mitotic rate. Molecular assays such as gene expression profiling have been explored as a means to refine risk stratification by incorporating tumor biology into decision-making.

The DecisionDx-Melanoma assay evaluates expression of 31 genes associated with melanoma tumor biology to provide prognostic information related to recurrence risk and metastasis. The i31-SLNB algorithm combines this molecular signal with selected clinical variables to estimate the probability of sentinel lymph node metastasis and support shared decision-making regarding SLNB.

The study expands on earlier prospective analyses evaluating the clinical performance of the 31-GEP–based test in melanoma. Prior studies have suggested that the assay may help inform SLNB decision-making and reduce potentially unnecessary procedures in selected patients while maintaining favorable outcomes.^3-5

The most recent update of the NCCN guidelines supported use of the Merlin clinicopathologic–gene expression profile in patients with stage T1b and T2a cutaneous melanoma as part of shared decision-making.²

The full analysis has been published in Future Oncology.⁶ Investigators noted that additional follow-up may further clarify long-term recurrence outcomes and the potential impact of incorporating molecular risk models into routine melanoma care.

REFERENCES

1. DecisionDx®-Melanoma’s i31-SLNB: Report from the Largest Prospective Multicenter Study to Date Confirms 2.6% Nodal Positivity in Patients Predicted to Have Less Than 5% Risk. News release. Castle Biosciences. March 9, 2026. Accessed March 12, 2026. https://tinyurl.com/rwsy3nkd

2. NCCN. Clinical Practice Guidelines in Oncology. Cutaneous melanoma, version 1.2026. Accessed March 12, 2026. https://tinyurl.com/5b39f96p

3. Yamamoto M, Sickle-Santanello B, Beard T, et al. The 31-gene expression profile test informs sentinel lymph node biopsy decisions in patients with cutaneous melanoma: results of a prospective, multicenter study. Curr Med Res Opin. 2023;39(3):417-423. doi:10.1080/03007995.2023.2165813
4. Guenther JM, Ward A, Martin BJ, et al. A Prospective, Multicenter Analysis of Recurrence-Free Survival After Sentinel Lymph Node Biopsy Decisions Influenced by the 31-GEP. Cancer Med. 2025;14(7):e70839. doi:10.1002/cam4.70839
5. Guenther JM, Ward A, Martin B, et al. A prospective, multicenter analysis of the integrated 31-gene expression profile test for sentinel lymph node biopsy (i31-GEP for SLNB) test demonstrates reduced number of unnecessary SLNBs in patients with cutaneous melanoma. World J Surg Oncol. 2025 Jan 3;23(1):5. doi: 10.1186/s12957-024-03640-x

6. Beard T, Guenther JM, Leong SP, et al. The integrated 31-gene expression profile test identifies low-risk patients with cutaneous melanoma who can forego the SLNB procedure: results from a prospective, multicenter trial. Future Oncol. Published online March 13 2026. doi: 10.1080/14796694.2026.2640227