Observational Analysis Of Ido-1 Expression In Mel Samples Assessed Using An Rnascope Assay.

53Background: IDO-1 catalyzes the degradation of trp to kyn and can promote tumor escape from host immunosurveillance. IDO-1 expression evaluation has potential importance in identification of a population with worse prognosis and is important in the clinical evaluation of IDO-1 inhibitors. We have developed an optimized assay for IDO-1 specific message detection using RNAscope technology (RST) and applied it to an analysis of human melanoma (MEL) samples. Methods: 25 MEL samples were evaluated for IDO-1 by IHC and the samples used to optimize the RST assay. IDO-1 expression could be demonstrated in tumor cells (TC) as well as in immune cells (IC) infiltrating the tumor and in IC in the peritumoral area. A scoring method was developed to classify IDO-1 expression in all three populations. An H-score of 5 or greater was used as an arbitrary cutoff for IDO-1 positivity. An additional 27 MEL samples, collected as part of the ECHO202/KN037 study of epacadostat in combination with pembrolizumab, were evaluated...