This primary endometrial carcinoma expresses which biomarkers?

• A. p53, CK20
• B. p63, PTEN
• C. p53, p16
• D. p16, PAX8

Answer: (C)

Endometrial carcinomas vary by subtype, and the high-grade serous form often shows dysfunction in key cell-cycle regulators. A TP53 mutation in serous tumors leads to abnormal p53 staining, usually strong and diffuse or completely absent, reflecting loss of normal p53 function. p16 overexpression frequently accompanies these high-grade tumors as part of broader deregulation of the RB pathway and cell-cycle control. Together, p53 and p16 positivity points toward a serous, primary endometrial carcinoma rather than a lower-grade endometrioid type, which tends to have a different profile (often with PTEN alterations and less p53/p16 overexpression). The other marker combinations are less characteristic: CK20 is more typical of colorectal/urothelial origins; p63 is associated with squamous differentiation; PTEN is more indicative of endometrioid tumors; PAX8 marks Müllerian origin but does not specifically define the serous/high-grade pattern as clearly as p53 with p16.