Is mismatch repair (MMR) deficiency more favorable than MMR proficiency in endometrial cancer?

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MMR Deficiency is More Favorable in Endometrial Cancer

MMR-deficient (MMRd) endometrial cancer has a better prognosis than MMR-proficient (MMRp) disease, particularly in terms of recurrence-free survival, and critically determines treatment selection for advanced/recurrent disease where MMRd tumors respond preferentially to immune checkpoint inhibitors.

Prognostic Implications

Overall Survival and Recurrence Patterns

MMRd tumors demonstrate superior outcomes compared to MMRp tumors in several key contexts:

  • Recurrence-free survival: MMRd patients show better recurrence-free survival, particularly in nonmetastatic disease 1. In a population-based study of 892 patients, MMRd status was associated with improved overall survival (HR = 0.38,95% CI 0.20-0.76, p = 0.006) in endometrial cancer, maintaining significance even after adjusting for age, stage, and grade (HR = 0.42,95% CI 0.20-0.88, p = 0.021) 1.

  • Nonendometrioid histology: Among patients with nonendometrioid tumors specifically, MMRd tumors had significantly lower recurrence (10.0% vs 42.0%, p = 0.001) and mortality rates (13.1% vs 36.1%, p = 0.01) compared to MMRp tumors 2.

  • Intermediate-risk disease: Following vaginal brachytherapy, MMRd patients had inferior 3-year recurrence-free survival (75% vs 96%, p = 0.001) compared to MMRp patients, though overall survival remained similar 3. This suggests MMRd may require different adjuvant strategies despite generally favorable biology.

Clinicopathologic Associations

MMRd tumors present with distinct features 4, 5:

  • More commonly endometrioid histology (87.9% vs 75.5%)
  • Higher rates of lymphovascular space invasion (27.2% vs 16.9%)
  • Despite more LVSI, fewer actual recurrences occur
  • Deep myometrial invasion more common
  • Lower rates of L1CAM positivity and p53 mutation

Treatment Selection Based on MMR Status

Advanced/Recurrent Disease (Most Critical Application)

The 2025 ESGO-ESTRO-ESP guidelines establish MMR status as the primary determinant for first-line systemic therapy 6:

  • MMRd tumors: Should receive immune checkpoint inhibitors (dostarlimab, durvalumab, or pembrolizumab) combined with carboplatin-paclitaxel chemotherapy, followed by immune checkpoint inhibitor maintenance therapy (Level I, Grade A evidence) 6.

  • MMRp tumors: Should receive carboplatin-paclitaxel chemotherapy for rapidly growing or symptomatic disease. Immune checkpoint inhibitors plus chemotherapy can be considered but with lower priority (Level I, Grade B evidence) 6.

  • Second-line therapy: For immune checkpoint inhibitor-naive MMRd patients, monotherapy with dostarlimab or pembrolizumab is the preferred option (Level III, Grade A) 6.

Early-Stage Disease Risk Stratification

The 2022 ESMO guidelines integrate MMR status into risk classification 7:

  • Low-risk: Stage IA (G1-G2) endometrioid with MMRd or NSMP (no specific molecular profile) and no/focal LVSI
  • Intermediate-risk: Stage IA G3 endometrioid with MMRd/NSMP and no/focal LVSI
  • High-intermediate risk: Stage I endometrioid (MMRd/NSMP) any grade with substantial LVSI

Clinical Pitfalls and Caveats

Context-Dependent Prognostic Value

The prognostic benefit of MMRd is not uniform across all treatment contexts:

  • In patients receiving adjuvant radiotherapy alone, MMR status showed limited prognostic impact on disease-free survival 8
  • Among intermediate-risk patients treated with vaginal brachytherapy, MMRd paradoxically showed worse recurrence-free survival 3
  • This suggests MMRd tumors may have different biology that responds variably to specific adjuvant modalities

Lynch Syndrome Screening

MMRd occurs in 20-40% of endometrial cancers 4, 9, with substantial proportions representing Lynch syndrome:

  • MLH1/PMS2 loss most common in sporadic cases
  • MSH2/MSH6 loss more strongly associated with Lynch syndrome
  • In patients under 50 years, approximately 46% of MMRd tumors were associated with germline mutations 10

Testing Considerations

Universal MMR testing should be performed on all endometrial cancers to:

  1. Identify Lynch syndrome candidates
  2. Guide immunotherapy eligibility in advanced/recurrent disease
  3. Refine risk stratification for adjuvant therapy decisions

The most critical application is determining eligibility for immune checkpoint inhibitors in advanced disease, where MMRd status predicts superior response and represents a Level I, Grade A indication for specific treatment 6.

References

2
Research

Endometrial Cancer Presentation and Outcomes Based on Mismatch Repair Protein Expression From a Population-Based Study.

International journal of gynecological cancer : official journal of the International Gynecological Cancer Society, 2018

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.