Imaging mass spectrometry-based proteomic approach for the differentiation between renal oncocytoma and chromophobe RCC

Background: Differential diagnosis of oncocytoma (RO) and chromophobe RCC (ChRCC) may be challenging. In most cases, exact diagnosis is possible by macroscopical appearance, H&E morphology and immunohistochemistry. However, some renal tumors may show overlapping morphologic features, requiring the use of further methods to reach a definitive diagnosis. We applied imaging mass spectrometry (IMS) to differentiate ChRCC from RO. Methods: Formalin-fixed paraffin-embedded tissues were used included ROs (N=57) and ChRCCs (N=45). The cases were reviewed by two pathologists and diagnosis was verified using immunohistochemistry. Tissues were deparaffinized, antigen retrieved, and subjected to in-situ trypsin digestion. An organic matrix solution was deposited onto the digested tissues using an automatic sprayer. Tissues were then subsequently analyzed with a MALDI/TOF-TOF instrument. Two sample groups including ROs and ChRCCs were created and subjected to spectral and statistical analysis using SCiLS Lab software. Peak selection was evaluated through statistical comparison (Wilcoxon/Kruskal-Wallis). Results: A Linear discriminant analysis (LDA) algorithm model was used for the classification study. LDA incorporated and evaluated 120 m/z species to generate a classification model able to discern ROs from ChRCCs with a cross validation accuracy of 93%. The LDA model was then applied to an independent test set that could classify the two tumor subtypes with an accuracy of 83%. Statistical comparison revealed a nearly 2-fold change alteration of seven statistical significant m/z peptide signals (1377.6, 1424.7, 1575.8, 1785.8, 1906, 1919, 2057), some of the which are in concordance with previous studies [1] Conclusions: Our findings provide a new molecular strategy to supplement the current histopathological analysis of the renal neoplasms aiding in the diagnosis of RO versus ChRCC. References 1. Steurer S, Seddiqi AS, Singer JM, Bahar AS, Eichelberg C, Rink M, Dahlem R, Huland H, Sauter G, Simon R, Minner S, Burandt E, Stahl PR, Schlomm T, Wurlitzer M, Schluter H (2014) MALDI imaging on tissue microarrays identifies molecular features associated with renal cell cancer phenotype. Anticancer Res 34:2255–2261