Abstract

Case 1: 37-year-old female patient with a lesion on the left distal posterior upper arm. Clinical impression was melanoma vs inflamed Spitz's nevus. Histopathological workup revealed a thin melanocytic proliferation with pagetoid spreading melanocytes. 23-GEP testing was utilized, which returned a result of ‘gene expression profile suggestive of malignant neoplasm’. The final diagnosis was malignant melanoma, 0.4 mm Breslow depth. The GEP result added confirmatory evidence to the histopathological review, resulting in a clear and actionable diagnosis. Case 2: 34-year-old male patient with a lesion on the right lateral malar cheek. Upon histopathological review, an atypical intradermal melanocytic proliferation was observed. Large pleomorphic melanocytes with large inclusions/pseudoinclusions, dusky, abundant cytoplasm, and some spitzoid features were noted. SOX10 immunohistochemistry (IHC) highlighted the melanocytes. PRAME staining showed diffuse (although patchy and weak) positivity that was stronger in the more superficial melanocytes with abundant pleomorphism in comparison to weaker staining in the deeper melanocytes. HMB45 IHC demonstrated patchy staining throughout but was also mostly positive in the larger, more pleomorphic melanocytes. Lastly, Ki-67 staining highlighted the more superficial melanocytes with a mitotic rate of 5-7%, while the deeper melanocytes were mostly negative. Based on these concerning ambiguous IHC results, 23-GEP testing was performed, which returned a result of ‘gene expression profile suggestive of malignant neoplasm’. The final diagnosis was malignant melanoma, 2.5 mm Breslow depth. Overall, the worrisome (yet inconclusive) features of malignancy identified during histopathological review were more definitively confirmed by GEP testing, facilitating final diagnoses of melanoma.

Financial Disclosure:

Speaker	Ineligible Company	Affiliation/Relationship	Ongoing/Ended	Role
Etan Marks, DO	Castle Biosciences, Inc.	Advisory Board, Consultant	Ongoing	Poster Presenter