confirmed the existence of heterogeneous MMR-protein expression (as described above) in 14 colorectal cancers; variant expression of antigenic determinant clusters, antigenic expression associated with different differentiation states, secondary mutational strikes occurring in specific tumor clones, and alterations in the tumor microenvironment (such as methylation, hypoxia, and oxidative stress) can lead to the heterogeneous expression of MMR proteins (5). This evidence concerns the gene MRC1 and colorectal cancer.