Microsatellite instability diagnosis using the fully automated Idylla platform: feasibility study of an in-house rapid molecular testing ancillary to immunohistochemistry in pathology laboratories.

Aim: To study the performances of the Idylla MSI Assay in the diagnosis of microsatellite instability (MSI) or microsatellite stability (MSS).

Methods: We selected 12 tumour samples previously tested for MSI focusing on cases with discrepant results between MLH1, PMS2, MSH2 and MSH6 immunohistochemistry and microsatellite molecular analyses (five cases) or doubtful immunohistochemistry (two cases). Idylla MSI Assay was compared with retrospective immunohistochemistry and molecular results.