Interpretation strategy of POLE, mismatch repair deficiency, and p53 in the multiple molecular classification of...

The 2023 FIGO staging system and current European guidelines incorporate four molecular classes of endometrial carcinoma: POLEmut, MMRd, p53abn, and NSMP. Tumours harboring multiple classifying alterations require hierarchical interpretation. This study evaluated the clinical impact of resolving multiple-classifier tumours according to the hierarchy POLEmut > MMRd > p53abn.

We retrospectively analyzed 512 consecutive surgically treated endometrial carcinomas diagnosed between September 2023 and April 2026. All cases underwent MMR and p53 immunohistochemistry and POLE exonuclease-domain sequencing. Clinicopathological features, tumour mutational burden, molecular reclassification, FIGO 2023 staging, adjuvant treatment implications, and survival outcomes were assessed.

Forty-two tumours (8.2%) were multiple classifiers, including MMRd-p53abn (n = 21), POLEmut-p53abn (n = 14), POLEmut-MMRd (n = 4), and triple-positive tumours (n = 3). Hierarchical resolution reclassified 38 cases (7.4%) that would otherwise have been categorized as p53abn. POLEmut-p53abn tumours resembled pure POLEmut tumours and showed no recurrence, whereas MMRd-p53abn tumours were clinically closer to MMRd cases. Subclonal p53 staining was more common in multiple-classifier tumours than pure p53abn tumours (55.3% vs. 9.0%). p53abn remained the strongest adverse predictor of overall survival.

Multiple-classifier endometrial carcinomas should be interpreted using the recommended molecular hierarchy to avoid clinically meaningful overclassification and potential overtreatment.