Recent data show that the endometrial cancer molecular taxonomy (DNA polymerase epsilon, catalytic subunit [POLE]-ultramutated, mismatch repair-deficient [MMRd], p53-abnormal, no specific molecular profile [NSMP]) also applies to OEC, and that OEC is enriched for Lynch syndrome–associated tumors, supporting routine MMR testing. Here, MRC1 is linked to endometrial cancer.