Diagnostic Performance of Four-Panel Immunohistochemistry for Detecting Mismatch Repair Deficiency in Korean Patients with Colorectal Cancer

We conducted this single-center, retrospective study to assess a concordance rate between the microsatellite instability (MSI) analysis and the immunohistochemistry (IHC) in a cohort of Korean patients with hereditary non-polyposis colorectal carcinoma (HNPCRC). A total of 251 patients (n = 251) were included in the current study, who comprise 149 men (59.4%) and 102 women (40.6%) and whose mean age was 64.6 ± 11.5 years old. In our series, MSI-high (MSI-H) and microsatellite-stable (MSS) were identified in 17 (6.7%) and 234 patients (93.3%), respectively. Concordance analysis showed a strong agreement between MSI status and IHC expression of mismatch repair (MMR) proteins. Of the 17 patients with MSI-H, 16 (94.11%) had a loss of expression of ³ one MMR protein in the IHC findings, while one patient (5.9%) with MSI-H retained an intact expression of all four MMR proteins. Moreover, of the 234 patients with MSS, four (1.71%) had a loss of expression of ³ one MMR protein in the IHC findings. Of the 20 patients with a loss of expression of ³ one MMR protein in the IHC findings, 16 (80%) and four (20%) were found to have MSI-H and MSS, respectively. By contrast, 231 patients retained an intact expression of all four MMR proteins, with only one case (0.4%) being MSI-H and the remaining 98.3% (n = 230) MSS. There were distinct associations between the pattern of IHC expression of MMR proteins and microsatellite status. The most frequent abnormal expression patterns include mutL homolog 1 (MLH1) (-) postmeiotic segregation increased 2 (PMS2) (-) (n = 7), all of which were MSI-H, and mutS homologs 2 (MSH2) (-) mutS homologs 6 (MSH6) (-) (n = 7), with six patients with MSI-H and one with MSS. PMS2 (-) alone was observed in three patients, one and two of whom were MSI-H and MSS, respectively. MSH6 (-) alone was observed in one patient with MSS. Finally, there were two patients with PMS2 (-) and MSH6 (-), both classified as MSI-H. The current study indicates the high concordance between IHC and MSI testing in HNPCRC. But this deserves further large-scale, prospective studies.