Long-Term Outcomes Support Utilization of 23-GEP in Clinically Ambiguous Melanocytic Neoplasms.

Difficult-to-diagnose melanocytic neoplasms often require additional diagnostic tools beyond histopathological assessment to reach a definitive diagnosis. The 23-gene expression profile (GEP) test provides additional diagnostic information, returning a result of suggestive of benign, intermediate, or suggestive of malignant. Here, we present a real-world cohort of ambiguous melanocytic lesions where the 23-GEP test was used to arrive at a definitive diagnosis with long-term follow-up. Melanocytic lesions were included in this study if 23-GEP testing was performed as part of their original diagnostic workup (n = 267). Long-term follow-up to determine disease recurrence and/or metastasis (ie, an event) was obtained (median, 6 years). 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, 2.9% for lesions with intermediate results, and 1.3% for lesions with benign results (Fisher exact, P = 0.002). Lesions with at least 5 years of clinical follow-up and/or an event (n = 163) had similar results to the overall cohort (P = 0.007). A benign 23-GEP result is associated with a low risk of recurrence/metastasis, whereas a malignant 23-GEP result is associated with a significantly higher risk of recurrence/metastasis, supporting the value of 23-GEP in guiding clinical management decisions for ambiguous melanocytic lesions.