The reported low percentage of dMMR BC may be influenced by the absence of a Companion Diagnostics assay (CDx) and/or tumor-specific guidelines for a MMR analysis and the different testing methods employed, such as direct sequencing of microsatellite markers, next-generation sequencing (NGS) and immunohistochemistry (IHC) for the four MMR proteins. Here, MRC1 is linked to neoplasm.