Molecular Testing in Endometrial Cancer

Primary Mutation Testing Algorithm

The National Comprehensive Cancer Network recommends that all endometrial tumors undergo immunohistochemical staining for MMR proteins (MLH1, MSH2, MSH6, PMS2) as part of routine pathologic examination, regardless of age, family history, or histologic features, to identify hereditary Lynch syndrome and predict response to immune checkpoint inhibitors in advanced/recurrent disease 1, 2
When MLH1 loss is detected, MLH1 promoter methylation testing should be performed immediately to distinguish sporadic (methylated) from hereditary (non-methylated) causes 1
POLE exonuclease domain mutation testing should be performed in all non-low-risk endometrial cancers to identify patients with excellent prognosis despite high-grade features 2
POLE-mutated tumors have excellent prognosis, with the best progression-free survival among all molecular subtypes, but favorable prognostic assignment should be restricted to validated hotspot POLE mutations 2, 3

The Cancer Genome Atlas identified four clinically significant molecular subtypes with distinct prognoses: POLE-mutated, MSI-H/hypermutated, copy number-low/microsatellite stable, and copy number-high/p53-abnormal 2, 3, 4
POLE-mutated tumors (7% of cases) have the best prognosis, while copy number-high/p53-abnormal tumors (26% of cases) have the worst prognosis 2, 3

MMR-deficient/MSI-H tumors are eligible for pembrolizumab monotherapy after progression on prior cytotoxic chemotherapy, with objective response rates of 48-57% in this population 5
Women with confirmed Lynch syndrome have a 30-60% lifetime risk of endometrial cancer and require annual endometrial biopsy starting at age 35 years, annual transvaginal ultrasound, and prophylactic hysterectomy with bilateral salpingo-oophorectomy at age 40 after childbearing completion 1
Annual colonoscopy for colorectal cancer surveillance is mandatory for patients with Lynch syndrome, as they have up to 80% lifetime risk of colorectal cancer 1

POLE-mutated tumors may not require adjuvant therapy despite high-grade features, though this remains under investigation 2
Copy number-high/p53-abnormal tumors almost always require chemotherapy as part of multimodality treatment 2
MSI-H tumors have intermediate prognosis and sensitivity to both chemotherapy and immunotherapy is under active investigation 2

Universal tumor testing for DNA mismatch repair (MMR) deficiency using immunohistochemistry should be performed on all newly diagnosed endometrial cancers, regardless of age, family history, or histologic features, to identify Lynch syndrome and guide treatment decisions 6
All endometrial tumors must undergo immunohistochemical staining for MMR proteins (MLH1, MSH2, MSH6, PMS2) as part of routine pathologic examination 6
When MLH1 loss is detected, perform MLH1 promoter methylation testing to distinguish between sporadic (epigenetic) and hereditary causes 6
Methylated MLH1 indicates sporadic cancer and does not require germline testing 6
Non-methylated MLH1 loss requires genetic counseling and germline mutation testing 6
Perform POLE exonuclease domain mutation testing in all non-low-risk endometrial cancers (intermediate, high-intermediate, high risk, or advanced disease) 6

Women with confirmed Lynch syndrome have 30-60% lifetime risk of endometrial cancer and require annual endometrial biopsy starting at age 35 years, annual transvaginal ultrasound, and prophylactic hysterectomy and bilateral salpingo-oophorectomy at age 40 after childbearing completion 6, 7, 8, 9
Annual colonoscopy for colorectal cancer surveillance is recommended for women with Lynch syndrome 6

Do not skip MLH1 methylation testing when MLH1 loss is detected—this distinguishes sporadic from hereditary cases and prevents unnecessary germline testing 6
Do not accept normal tumor MMR testing as excluding Lynch syndrome in patients with strong family history—9.5% of germline mutation carriers have tumor testing suggesting sporadic cancer 6

The complete molecular classification combines MMR status, p53 status, POLE mutation status, and traditional pathologic parameters, providing reproducible, prognostically relevant classification that guides adjuvant treatment decisions and improves risk stratification beyond traditional histopathologic features alone 6