Objectives. Beginning in 2014, the Society of Gynecologic Oncology and the American College of Obstetricians and Gynecologists have recommended universal tumor testing for mismatch repair deficiency in endometrial cancer. Mismatch repair testing can triage patients who may benefit from genetic testing for Lynch syndrome. Many women previously diagnosed with endometrial cancer have not undergone mismatch repair tumor testing. We sought to determine the feasibility of retroactive assessment for mismatch repair deficiency among women with diagnosed with endometrial cancer prior to 2014. Methods. Between 2016 and 2018, we identified 36 patients presenting for gynecologic oncology follow-up visits who were previously diagnosed with endometrial cancer. The endometrial pathology underwent tumor assessment for loss of expression of mismatch repair proteins by immunohistochemistry. Patients with abnormal mismatch repair testing were referred to genetic counseling and, if indicated, for germline genetic testing. Results. Thirty-six patients underwent retroactive tumor immunohistochemistry, yielding 10 (28%) abnormal results, including nine (25%) with loss of one or more mismatch repair proteins and one with inconclusive staining (2.8%). All ten patients with abnormal immunohistochemistry were referred to genetic counseling; 9 (90%) accepted the referral and proceeded with genetic testing. One pathogenic mutation was identified in CHEK2 (11%). Five patients (56%) were found to have a variant of unknown significance. Conclusions. Implementation of universal retroactive tumor testing for mismatch repair deficiency in patients previously diagnosed with endometrial cancer is feasible. With the growing use of new molecular classification protocols for endometrial tumors, identification of mismatch repair deficiency may have significant clinicopathologic implications.
5 Understanding the clinical implication of mismatch repair deficiency in endometrioid endometrial cancer through a prospective study
