From Molecular Classification to Hereditary Cancer Syndrome Identification in Endometrial Cancer

Background: Endometrial carcinoma (EC) is one of the most common gynaecological malignancies, with a steadily increasing incidence worldwide. In 2013, a novel molecular classification of ECs enabled patient stratification into four groups with important clinical management implications: (1) DNA Polymerase Epsilon (POLE)-mutated, (2) microsatellite instability-high (MSI-H/dMMR) hypermutated, (3) tumours with low somatic copy number alteration (low-SCNA), and (4) tumours with high SCNA and p53 deficiency. This molecular classification should also be used as a tool to identify hereditary cancer syndromes, as MSI-ECs can be associated with Lynch Syndrome (LS, ORPHA:144) while somatic POLE mutations may reflect polymerase proofreading-associated polyposis (PPAP syndrome, ORPHA:447877). Methods: From 2022 to 2024, molecular classification of ECs was routinely performed on 188 consecutive cases. The results were correlated with family history and constitutional genetic testing. Results: Somatic testing revealed that 45 ECs were dMMR and 23 carried POLE variants. Five POLE-mutated ECs also displayed concomitant MSI. For all 68 patients, cancer genetic counselling was proposed, but only 41 accepted, and of these, 26 patients were eligible for the genetic test. None of the POLE somatic variants were proven to be constitutive, whereas LS was diagnosed in seven patients with dMMR-EC; interestingly, two of these patients displayed a POLE-mutated EC. Conclusions: Our data strongly suggest that molecular classification of ECs is important to improve the identification of LS and highlight the relevance of investigating all molecular markers at once in order to identify overlaps between POLE mutations and MMR defects.