N77: Correlation Of Immunohistochemical Mismatch Repair Protein Status In Colorectal Carcinoma Endoscopic Biopsy And Resection Specimens

É. Ryan2, O. O’Brien1, B. Creavin2, M. E. Kelly2, H. M. Mohan2, R. Geraghty1, K. Sheahan1, D. C. Winter2

1 – Department of Histopathology, St. Vincent’s University Hospital, Dublin, Ireland. 2 – Department of Surgery, St. Vincent’s University Hospital, Dublin, Ireland.

 

Aim: Microsatellite instability (MSI) is reflective of a deficient mismatch repair system (dMMR) and occurs in 15% of all colorectal carcinomas (CRC). This most frequently occurs due to sporadic or constitutional mutations in mismatch repair genes. Mismatch repair (MMR) status is often identified by immunohistochemistry (IHC) for mismatch repair proteins (MMRPs) on CRC resection specimens.  IHC testing performed on endoscopic biopsy material may be as reliable as that performed on resected specimens. We aimed to evaluate the reliability of MMR IHC staining on preoperative CRC endoscopic biopsies.

Method: A retrospective search of our institution’s histopathology database was performed. Patients with CRC who had MMR IHC performed on both their preoperative endoscopic biopsy and surgical resection from 2010 – 2016 were included. Concordance of MMR staining between these specimens was assessed.

Results: 53 patients had MMR IHC performed on both their preoperative endoscopic biopsy and resection specimens; 10 patients (18.87%) demonstrated loss of 1 or more MMRP on their endoscopic tumour biopsy. The remainder (81.13%)demonstrated preservation of staining for all MMRPs. There was 100% agreement in MMR IHC status between specimens in all cases (κ = 1.000, p < 0.000), with a sensitivity of 100% (95% confidence interval [CI]: 69.15-100] and specificity 100% (95% CI: 91.78-100) for detection of dMMR.

Conclusion: Endoscopic biopsies may provide a suitable source of tissue for MMR IHC analysis. This could allow a number of advantages to both clinicians and patients in the management of CRC.

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