Track: Clinical Studies

Abstract:

Background: Difficult-to-diagnose melanocytic neoplasms can require additional diagnostic tools beyond histopathological assessment to reach a definitive diagnosis. The 23-gene expression profile (GEP) test provides additional diagnostic information by analyzing the expression of 23 genes, returning a result suggestive of benign, intermediate, or suggestive of malignant. Here, within a real-world cohort of difficult-to-diagnose lesions, the ability of 23-GEP to contribute towards a definitive diagnosis and its performance using long-term outcomes is described.

Methods: Melanocytic lesions were included in this study if they were deemed ambiguous by a board-certified dermatopathologist at a single large institution and obtained 23-GEP testing as part of their diagnostic workup (n=267). Long-term follow-up to determine disease recurrence and/or metastasis (i.e., an event) was obtained (median, 6 years).

Results: Following 23-GEP testing, 89.5% of difficult-to-diagnose lesions were provided definitive diagnoses. Event rates were 11.5% for lesions with malignant 23-GEP results (n=78), 2.9% for lesions with intermediate results (n=34), and 1.3% for lesions with benign results (n=155) (Fisher’s exact, p=0.002). Similar results were obtained with lesions with at least ≥5 years of follow-up and/or an event (n=163) (p=0.007).

Conclusions: A benign 23-GEP result is associated with a low risk of recurrence/metastasis, supporting its value in guiding clinical management decisions for ambiguous melanocytic lesions. The use of 23-GEP testing in difficult-to-diagnose cases can both reduce diagnostic uncertainty and identify patients likely to sustain excellent 5-year outcomes that can inform appropriate risk-aligned treatment strategies for this challenging subset of melanocytic tumors.