Transcriptional differences between canine cutaneous epitheliotropic lymphoma and immune-mediated dermatoses

Background – Canine cutaneous epitheliotropic T cell lymphoma (CETL) and immune-mediated T cell predominant dermatoses (IMD) share several clinical and histopathological features, but differ substantially in prognosis. Diagnostic discrimination of early lesions may be challenging, as molecular differences are not fully unravelled and reliable discriminatory markers are lacking. Hypothesis/Objectives – We hypothesized that the gene expression profile of CETL and IMD is significantly different. Aim of this study was to uncover these transcriptional differences, and to identify candidate markers to discriminate ambiguous CETL and IMD cases. Animals – This retrospective study was performed with formalin-fixed and paraffin-embedded skin biopsies from dogs with CETL (n= 9) and IMD (n= 11), respectively, with clinical follow-up available. Methods – RNA extracted from the biopsies was sequenced in 100bp single-end cycles. DESeq2 was used for principal component (PCA) and differential gene expression analysis. Genes with significantly different expression were analyzed for enriched pathways using two different tools. The expression of six selected genes and two proteins was validated by RT-qPCR and by immunohistochemistry. Results – PCA demonstrated a separation of CETL from IMD cases with respect to gene expression. 503 genes were upregulated, while 4986 were downregulated in CETL compared to IMD. RT-qPCR confirmed the sequencing results for 5/6 genes tested, while immunohistochemistry was not entirely consistent. Conclusions and clinical importance – Our study unraveled transcriptional differences between canine CETL and IMD, and showed some similarities with human cutaneous lymphoma studies. The diagnostic value of the candidate markers tested remains open and needs further evaluation with a larger sample number.