From a total of 104 patients with colorectal cancer, immunohistochemical analysis of the expression of all four MMR proteins showed that heterogeneous expression of MMR proteins (as well as deficient immunoreactivity of tumor cells (Figure 1) was present in 12 cases, while proficient expression of MMR proteins was detected in 80 tumors (Figure 2). The gene discussed is MRC1; the disease is colorectal cancer.