537PAssessment of local clinical practice for testing of mismatch repair deficiency in metastatic colorectal cancer: The need for new diagnostic guidelines prior to immunotherapy. (23rd October 2018) - Cohen, R; Hain, E; Buhard, O; Guilloux, A; Bardier, A; Kaci, R; Bertheau, P; Renaud, F; Bibeau, F; Fléjou, J-F; André, T; Svrcek, M; et al.