While most ECs can be classified based on a single-classifier (POLE exonuclease domain mutations - POLEmut, MMR deficiency - MMRd, p53 abnormal - p53abn), a small but clinically relevant group of tumours harbour more than one molecular classifying feature and are referred to as "Multiple classifier" ECs.
For endometrial cancer, four molecular subgroups have undergone extensive studies in recent years: POLE ultramutated (POLEmut), mismatch repair-deficient (MMRd), p53 mutant (p53abn) and those EC lacking any of these alterations, referred to as NSMP (non-specific molecular profile).
After The Cancer Genome Atlas (TCGA) findings, four novel prognostic groups may direct the management of endometrial cancer (EC): POLE-mutated/ultramutated (POLEmt), microsatellite-instable/hypermutated (MSI), copy-number-low/p53-wild-type (p53wt), and copy-number-high/p53-mutated (p53mt).
We identify four molecular subtypes that resemble those observed in endometrial carcinoma: POLE-mutated, microsatellite instability, copy number high, and copy number low subtypes.
This study provides significant evidence that analyses of proofreading POLE mutations and MSI status based on mononucleotide repeat markers are potentially useful biomarkers to identify EC patients with better prognosis.
Sensitivity to radiotherapy and selected chemotherapeutics was compared between <i>Pole</i>-mutant mouse-derived embryonic stem (mES) cells, generated using CRISPR-Cas9 (<i>Pole</i> mutations D275A/E275A, and cancer-associated P286R, S297F, V411L) and isogenic wild-type cell lines.<b>Results:</b> In the observation arm of the PORTEC-1 trial (<i>N</i> = 245), women with <i>POLE</i>-mutant endometrial cancers (<i>N</i> = 16) had an improved recurrence-free survival (10-year recurrence-free survival 100% vs. 80.1% for <i>POLE-</i>wild-type; HR, 0.143; 95% confidence interval, 0.001-0.996; <i>P</i> = 0.049).
To gain insight into the pathogenesis of these tumors we have analyzed the immunophenotype (ARID1A, MLH1, PMS2, MSH2, MSH6, p53, β-catenin, SMARCB1, synaptophysin, chromogranin A, and CD56) and mutational status (PTEN, KRAS, PIK3CA, TP53 and POLE) of 4 dedifferentiated endometrial carcinomas with strong and diffuse neuroendocrine expression.
We focused on low-grade, non-ultramutated tumours as these tumours have a worse prognosis than the ultramutated POLE-positive endometrioid endometrial carcinomas (EECs).
In our study, 151 endometrial carcinomas were molecularly categorized using sequencing for the exonuclease domain mutations (EDM) of POLE, and immunohistochemistry for p53 and mismatch repair (MMR) proteins.
Forty-nine ECs (three tumour blocks/case) were selected with alterations in POLE (n=10), CTNNB1 (n=8), p53 (n=10), mismatch repair (n=11), L1CAM (n=10), and ECs without any of these markers (n=9).
Breast cancer (BRCA)-mutated high-grade serous ovarian cancers, clear cell ovarian cancers with microsatellite instability (MSI), POLE ultramutated and MSI hypermutated endometrial cancers are likely to be sensitive to programmed cell death (PD-1)/PD-ligand 1 (PD-L1) pathway blockade, since these tumors show increased neoantigen load, increased CD8<sup>+</sup> TIL number and PD-1 and PD-L1 overexpression.
POLE-mutated undifferentiated and dedifferentiated endometrial carcinomas were more frequently stage I tumors than similar carcinomas lacking exonuclease domain mutations (7/9; 78% vs. 3/12; 25%; P=0.023) and patients had significantly better outcome (disease-specific survival) than those without POLE exonuclease domain mutations (P=0.02).
Analysis of MSI, hotspot mutations in 14 genes including POLE, protein expression of p53, ARID1a, β-catenin, L1CAM, PTEN, ER, and PR was undertaken on 947 available early-stage endometrioid endometrial carcinomas from the PORTEC-1 and -2 trials, mostly high-intermediate risk (n = 614).
According to The Cancer Genome Atlas classification, we distributed 95% of the undifferentiated carcinomas in this series as follows: (a) hypermutated tumors with loss of any mismatch repair protein expression and microsatellite instability (eight cases, 45%); (b) ultramutated carcinomas carrying mutations in the exonuclease domain of POLE (two cases, 11%); (c) high copy number alterations (copy-number high) tumors group exhibiting only TP53 mutations and high number of alterations detected by FISH (two cases, 11%); and (d) low copy number alterations (copy-number low) tumors with molecular alterations typical of endometrioid endometrial carcinomas (five cases, 28%).
In univariable analysis, POLE-mutated endometrial carcinomas had significantly improved outcomes compared with patients with no EDMs for PFS, DSS, and OS.
Mean BMI was statistically different between the ECs in the CNL (35.8) versus POLE (29.8) cluster (p=0.006) and approached significance for the MSI (33.0) versus CNL (35.8) cluster (p=0.05).
Ultramutated POLE proofreading-mutant endometrial cancers are characterized by a robust intratumoral T-cell response, which correlates with, and may be caused by an enrichment of antigenic neopeptides.