Mass Spectrometry Imaging of Melanocytic Lesions

Introduction Melanocytic skin lesions often share similar and overlapping histologic features from which a diagnosis can be challenging even among expert dermatopathologists. In this study mass spectrometry imaging (MSI) technology was used to distinguish nevi from melanoma lesions based on their molecular characteristics. In addition, melanoma tissues carrying BRAF and NRAS mutations were investigated to detect proteomic differences in melanoma with a specific mutational background. Method 3 μm thin sections of formalin-fixed paraffin-embedded skin tissues were cut and mounted onto conductive glass slides for IMS analysis and on regular slides for hematoxylin and eosin (HE) staining. Diagnosis was performed with two concordant histopathological evaluation by board-certified pathologists. Sections for IMS analysis were processed and analyzed with a rapifleX MALDI Tissuetyper mass spectrometer as described earlier [1]. The histology images were previously annotated in the melanocytic areas and merged to the IMS sections. Spectra were imported into SCiLS Lab software and R for data processing and analysis. Results Several peptide features were found to be differentially expressed between melanoma and nevi (ROC ≥ 0.7) and were used to build a linear discriminant analysis (LDA) classification model that could discriminate melanoma from nevi with a sensitivity of 96% and a specificity of 100% on a training set (113 patients), and a sensitivity of 91% and a specificity of 95% on a testing set (90 patients) . Proteomic signatures were obtained discriminating melanoma with from without BRAF and NRAS mutations with high accuracy 94%. Conversely, BRAF and NRAS mutated melanomas showed a similar proteomic signature and the accuracy to discriminate both was only 71% [2]. Among the differentially expressed peptides, vimentin, histones H2B and H4 were identified upregulated while 3-methyladenine DNA glycosylases and collagen alpha-1(I) downregulated in the melanoma compared to nevi tissues. Conclusion We demonstrated that MSI is able to differentiate on a proteomic level malignant melanomas from benign melanocytic nevi. MSI based-proteomic differences in melanoma with a specific mutational background were demonstrated which could provide a framework to explore these changes among melanoma subtypes. References [1] Casadonte, R.; Kriegsmann, M.; Kriegsmann, K.; Hauk, I.; Meliß, R.R.; Müller, C.S.L.; Kriegsmann, J. , (2021), Imaging Mass Spectrometry- Based Proteomic Analysis to Differentiate Melanocytic Nevi and Malignant Melanoma, MDPI, Cancers (Basel), Basel, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8267712/ [2] Rita Casadonte, Mark Kriegsmann, Katharina Kriegsmann, Helene Streit, Rolf R. Meliß, Cornelia S.L. Müller, Joerg Kriegsmann, (2023), Imaging Mass Spectrometry for the Classification of Melanoma Based on BRAF/NRAS Mutational Status, MDPI, Int. J. Mol. Sci, Basel, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10049262/