Pathologist-recommended molecular testing in endometrial cancer: A single-institution experience highlighting the recognition of POLE-Mutated carcinomas in post-menopausal and advanced stage patients, immunohistochemical pitfalls, and other clinically significant findings.

Endometrial carcinomas cluster based on mismatch repair (MMR), TP53, and POLE exonuclease domain mutation status. Although TP53 and MMR deficiency have immunohistochemical surrogates, molecular testing is required to determine POLE status. Pathologists can identify candidates based on morphologic and immunohistochemical findings, however the outcome and limitations of pathologist-recommended molecular testing have not been investigated. We evaluated endometrial carcinomas diagnosed from 1/2022-9/2025 in which molecular testing was recommended in the pathologist's comment. Sequencing was recommended in 38 and pursued in 16 (42%). Testing impacted classification in 50% (8/16): four were POLE-mut, and four were TP53-abnormal (p53-abn) or MMR-deficient (MMRd) with molecular findings discordant with immunostaining. All POLE-mut cases were multiple classifiers diagnosed in patients >50; half were stage III; POLE-mut status down-staged one. Impactful immunohistochemical-molecular discordances occurred in two p53-abn and two no specific molecular profile (NSMP) tumors. Other unexpected molecular findings included an NSMP carcinoma with a BRCA2 mutation leading to confirmation of a germline syndrome and an MMR-deficient malignancy with TSC2 alterations which was reclassified from high-grade carcinoma to malignant PEComa. Adverse outcomes were seen in 0% of POLE-mut, 33% of p53-abn, and 67% of NSMP carcinomas. These findings suggest potential value of pathologist-directed molecular testing for identifying POLE-mut endometrial cancers, particularly in post-menopausal patients with abnormal p53 and high-grade histology, and in selected stage III patients, in whom these features might not prompt clinical consideration for molecular work-up. They also illustrate limitations of immunohistochemical surrogates and ProMisE classification, the potential for aggressive behavior in NSMP tumors with POLE-like histomorphology, and the role of molecular testing in identifying clinically impactful mutations beyond POLE.