Diagnostic utility of the 23-gene expression profile test for an atypical intradermal melanocytic proliferation.

Ancillary tests such as immunohistochemistry (IHC) and gene expression profile (GEP) testing may be needed to arrive at a definitive diagnosis for some atypical melanocytic neoplasms. A 34-year-old male with a family history of melanoma presented with a large, heterogeneous melanocytic lesion on the cheek. Histopathological review of two biopsies revealed an atypical intradermal melanocytic proliferation with spitzoid features without ulceration or regression. Scattered mitotic figures were identified. In addition to performing SOX10 IHC, PRAME and HMB45 staining highlighted weak, patchy positivity that was stronger in superficial, pleomorphic melanocytes (Ki-67, 5-7% mitotic rate). Based on these concerning but ambiguous IHC results and lingering concern for melanoma reiterated by other consulting dermatopathologists, the 23-GEP was requested for both specimens, which both returned a malignant result. The inconclusive histopathological features of malignancy were resolved by 23-GEP testing, facilitating a final diagnosis of malignant melanoma (pT3a, 2.5 mm Breslow depth, Clark's level IV).