This exhaustive definition enabled the inclusion of the MSI-Low category, for which the diagnostic value for MMR deficiency is controversial22,23, all immunostaining profiles different from the loss of MLH1/PMS2 or MSH2/MSH6 and all cases with a discordance between the IHC and MSI-PCR results. The gene discussed is MSH6; the disease is mismatch repair cancer syndrome 1.