The hypothesis of dMMR status as a predictor of efficacy of PD1 inhibitors was tested in a phase 2 study of pembrolizumab on patients with dMMR mCRC, mismatch repair-proficient (pMMR) mCRC, and dMMR cancers other than those of the colorectum [52,53,54,55]. The gene discussed is PDCD1; the disease is cancer.