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P71 Does mismatch repair (MMR) deficiency have prognostic significance in low-risk endometrioid endometrial cancers?
  1. SR Kim1,
  2. A Pina2,
  3. A Albert3,
  4. J McAlpine4,
  5. R Wolber5,
  6. B Gilks5,
  7. M Carey4 and
  8. J Kwon4
  1. 1Gynecologic Oncology, University of British Columbia, Vancouver, BC
  2. 2Division of Gynecology Oncology, Universite de Montreal, Montreal, QC
  3. 3Women’s Health Research Institute
  4. 4Division of Gynecologic Oncology
  5. 5Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada


Introduction/Background Mismatch repair deficiency (MMRd) is observed in 25–30% of all endometrial cancers. This can be detected by the absence of MMR protein staining on immunohistochemistry (IHC). Only 10% of women with MMRd have Lynch syndrome, but MMRd may still have prognostic significance. The objective of this study was to compare clinical outcomes between MMR deficient and proficient low-risk endometrioid endometrial cancers (stage IA, grade 1/2).

Methodology This was a retrospective population-based cohort study of all low-risk endometrial cancers from Vancouver Coastal Health authority region from 2011 to 2016 that were assessed for MMR deficiency. Primary outcome measures were recurrence rates expressed per person-years (py), progression free survival (PFS) and overall survival (OS) calculated using Kaplan-Meier method and log-rank tests. Cox proportional hazards model estimated the association between MMRd and recurrence/death after adjustment for covariates.

Results There were 477 low-risk patients, including 132 MMRd (27.7%) and 345 MMRp (proficient) patients. Women with MMRd tumors had higher recurrence rates (3.53p100py vs 1.21p100py) and worse PFS (p=0.0086) compared to women with MMRp tumors. After adjustment for age, LVSI status, adjuvant therapy, and post-operative grade, MMRd status remained associated with a higher risk of recurrence (HR 2.99, 95% CI 1.27–7.04). There was no significant difference in OS between MMR groups (HR 1.38, 95% CI 0.57–3.33).

Conclusion In low-risk stage IA grade 1 or 2 endometrioid endometrial cancers, MMR deficiency is associated with a higher recurrence rate than in MMR proficient cases, after adjustment for covariates, implying that MMR deficiency reflects a different biology in endometrial cancer.

Disclosure Nothing to disclose.

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