Knowledge of tumour MMR status is also important because it can influence treatment; the adjuvant 5-flurouracil confers no survival benefit in MMR-deficient CRC [10,11], MMR-deficient metastatic CRC responds much better to capecitabine and oxaliplatin [12], and MMR-deficient tumours respond better to the programmed cell death protein 1 (PD-1) inhibitor pembrolizumab [13,14]. The gene discussed is MRC1; the disease is colorectal carcinoma.