A comparative analysis of MMR immunohistochemistry panels: Evaluating the utility of four-protein versus two-protein panels in endometrial cancer patients.

Aims: This study aimed to assess the accuracy of a two-protein panel for mismatch repair (MMR) immunohistochemistry (IHC) compared to a four-protein panel in a cohort of endometrial cancer patients.

Methods: The study included patients diagnosed with endometrial cancer between January 2018 and December 2023 with patients underwent MMR IHC staining for the four-protein panel (MSH2, MSH6, MLH1, and PMS2) serving as the reference standard. Various combinations of two proteins were examined and evaluated for their accuracy against the four-protein panel. Sensitivity, negative predictive value (NPV), and negative likelihood ratio were calculated for each combination. McNemar's test was performed to assess discordance, and receiver operating characteristic (ROC) curves were generated to evaluate diagnostic accuracy.

Results: Of 593 patients, MMR deficiency defined as at least one protein loss was observed in 146 patients (24.62%). When compared with four-protein panel, the highest sensitivity was observed with the MSH6/PMS2 combination (99.32%), followed sequentially by MSH6/MLH1 (97.26%), MSH2/PMS2 (93.15%), MSH2/MLH1 (91.10%), MLH1/PMS2 (79.45%), and MSH2/MSH6 (21.92%). The MSH6/PMS2 combination also demonstrated the best NPV of 99.78% and negative likelihood ratio of 0.01, while MSH6/MLH1 showed satisfactory NPV of 99.11% and negative likelihood ratio of 0.03. McNemar's test revealed no statistical difference between the four-protein panel and the MSH6/PMS2 panel (p = 1.000), and the MSH6/MLH1 panel (p = 0.125).

Conclusions: The two-protein panel, particularly MSH6/PMS2, offers high sensitivity and negative predictive value, suggesting its potential as a cost-effective alternative to the four-protein panel in MMR testing for endometrial cancer patients.