MRC1 and undifferentiated carcinoma of esophagus: MMR loss by IHC has been reported in 3-6.6% of esophageal adenocarcinomas18 and in a separate study determined that the MSI-H rate in esophageal squamous cell carcinoma and adenocarcinomas is 0.6%.19 The rate of MMR loss in SMARCA4 undifferentiated carcinomas of the esophagus has not been characterized; however, elsewhere in the GI system, case reports of MMR loss in SMARCA4-deficient carcinomas have been demonstrated.