TP53 and neoplasm: This case illustrates how routine immunohistochemistry can provide important insights into underlying molecular events in cancers, exemplifies an uncommon co-existence of a DNA mismatch repair protein deficiency and a p53-aberrant immunophenotype in low-grade endometrioid carcinoma, illustrates morphologic differences between p53-aberrant and p53-wild type areas in the same tumor, and is exemplary of the emerging theory that lymph node metastases may be comprised of different subclones of the primary tumor.