Objectives For synchronous endometrial and ovarian cancers, most centers rely on mismatch repair testing of the endometrial cancer to identify Lynch syndrome, and neglect the ovarian tumor site completely. We examined the mismatch repair immunohistochemistry and microsatellite instability results from the endometrium and ovary to assess discordance between the tumor sites and between tests.
Methods 30 women with newly diagnosed synchronous endometrial and ovarian cancer were prospectively recruited from three cancer centers in Ontario, Canada. Both tumor sites were assessed for mismatch repair deficiency by immunohistochemistry and microsatellite instability test; discordance in results between tumor sites and discordance between test results at each site was examined. Cases with discordant results had tumors sequenced with a targeted panel in order to reconcile the findings. All women underwent mismatch repair gene germline testing.
Results Of 30 patients, 11 (37%) were mismatch repair deficient or microsatellite instable at either tumor site, with 5 (17%) testing positive for Lynch syndrome. Mismatch repair immunohistochemistry expression was discordant between endometrial and ovarian tumor sites in 2 of 27 patients (7%) while microsatellite instability results were discordant in 2 of 25 patients (8%). Relying on immunohistochemistry or microsatellite instability alone on the endometrial tumor would have missed one and three cases of Lynch syndrome, respectively. One patient with Lynch syndrome with a PMS2 pathogenic variant was not detected by either immunohistochemistry or microsatellite instability testing. The rate of discordance between immunohistochemistry and microsatellite instability test was 3.8% in the ovary and 12% in the endometrium.
Conclusions There was discordance in immunohistochemistry and microsatellite instability results between tumor sites and between tests within each site. Endometrial tumor testing with mismatch repair immunohistochemistry performed well, but missed one case of Lynch syndrome. Given the high incidence of Lynch syndrome (17%), consideration may be given to germline testing in all patients with synchronous endometrial and ovarian cancers.
- lynch syndrome II
- uterine cancer
- ovarian cancer
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Contributors SRK: data curation, formal analysis, project administration, visualization, writing—original draft, and writing—review and editing. AT: conceptualization, data curation, investigation, methodology, and writing—review and editing. RK, MC, BC, AL, JL-E, and AP: investigation and writing—review and editing. LE, DV: investigation, resources, and writing—review and editing. TH, MA, and SH: resources and writing—review and editing. MM and LO: formal analysis and writing—review and editing. SG, MQB, and AMO: conceptualization and writing—review and editing, BD: writing—review and editing. EV: data curation, project administration, and writing—review and editing. TJP: formal analysis, investigation, and writing—review and editing. SEF: conceptualization, formal analysis, funding acquisition, project administration, investigation, methodology, supervision, and writing—review and editing.
Funding We have received funding from the Canadian Cancer Society (grant No 704038).
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval Institutional research ethics board approval was obtained from all three study sites.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information.
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