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Poster
IGCS20_1275
263 Discordant mismatch repair protein expression in synchronous endometrial and ovarian cancers
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  1. S Kim1,
  2. A Tone2,
  3. A Pollett3,
  4. R Kim4,
  5. M Cesari3,
  6. B Clarke3,
  7. L Eiriksson5,
  8. T Hart6,
  9. S Holter7,
  10. A Lytwyn8,
  11. M Maganti9,
  12. L Oldfield10,
  13. T Pugh10,
  14. S Gallinger11,
  15. M Bernardini1,
  16. A Oza12,
  17. V Dube3,
  18. J Lerner-Ellis3,
  19. E Van de Laar2,
  20. D Vicus1 and
  21. S Ferguson1
  1. 1Department of Obstetrics and Gynecology, University of Toronto, Canada
  2. 2Division of Gynecologic Oncology, Princess Margaret Cancer Centre/University Health Network/Sinai Health Systems, Canada
  3. 3Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada
  4. 4Fred A Litwin Family Centre for Genetic Medicine, University Health Network, Canada
  5. 5Division of Gynecology Oncology, Department of Obstetrics and Gynecology, Juravinski Cancer Centre, McMaster University, Canada
  6. 6Department of Psychology, Ryerson University, USA
  7. 7Zane Cohen Centre for Digestive Diseases, Familial Gastrointestinal Cancer Registry, Mount Sinai Hospital, Canada
  8. 8Division of Anatomical Pathology, Department of Pathology and Molecular Medicine, McMaster University, Canada
  9. 9Department of Biostatistics, Princess Margaret Cancer Centre/University Health Network, University of Toronto, Canada
  10. 10Department of Medical Biophysics, University of Toronto, USA
  11. 11Division of General Surgery, Princess Margaret Cancer Centre/University Health Network/Sinai Health Systems, Canada
  12. 12Division of Medical Oncology and Hematology, Princess Margaret Cancer Centre/University Health Network/Sinai Health Systems, Canada

Abstract

Objectives There is no established screening strategy for Lynch syndrome (LS) in synchronous endometrial (EC) and ovarian cancers (OC). Most centers use mismatch repair (MMR) immunohistochemistry (IHC) on endometrium only. We aim to examine the concordance in MMR expression between tumor sites in synchronous EC/OC.

Methods Thirty women with newly diagnosed synchronous EC/OC were prospectively recruited from three cancer centers in Ontario, Canada. Tumor sites were assessed for MMR deficiency by IHC and MSI testing. All women underwent germline testing for MMR mutations.

Results Out of 30 cases, twelve cases (40%) were either MMRd or MSI-H, with 5 (17%) confirmed to have a pathogenic germline mutation: 3 MSH6, 1 MLH1 and 1 PMS2. MMR testing by IHC took place in both ovary and endometrium in 27 cases and results were discordant between two sites in 2 cases (7%). MSI testing in both sites took place in 24 cases, and results were discordant in 2 cases (8%). Out of the 5 cases with confirmed LS, performing IHC alone on endometrium would have missed the diagnosis in 1 case, and performing MSI testing alone on endometrium would have missed the diagnosis in 3 cases, which all had a MSH6 mutation. One case of LS was missed by both IHC and MSI testing.

View this table:
Abstract 263 Table 1

Concordance of mismatch repair (MMR) immunohistochemistry (IHC) and microsatellite instability (MSI) results between ovary and endometrium for five cases with Lynch syndrome

Conclusions The incidence of LS was high in women with synchronous EC/OC (17%). Given the discordance in IHC and MSI results at the two tumor sites, consideration should be given to direct germline testing in all cases of synchronous EC/OC.

https://doi.org/10.1136/ijgc-2020-IGCS.226

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