To investigate the difference and consistency between MMR and PD-L1 in stage Ⅱ colorectal cancer (CRC).

A total of fifty patients performed operation from January 2016 to October 2017 and diagnosed as stageⅡCRC were enrolled in the study. The expression of MMR (MutL homolog 1 (MLH1)、MutS homolog 2 (MSH2)、MutS homolog 6 (MSH6)、Postmeiotic segregation increased 2 (PMS2) and PD-L1 were detected by immunohistochemistry, and the association between MMR and PD-L1 were analyzed.

The rate of dMMR and of PD-L1 positive cases was 32% (16/50) and 39% (19/50) in total CRC specimens. 20% (10/50) positive PD-L1 patients had dMMR tumors. The expression of PD-L1 was higher in the dMMR group than in the pMMR group, the difference between the two groups was statistically significant [62.5% (10/16) vs 26.5% (9/34), χ2=5.995, P=0.027]. The expression of PD-L1 was associated with MLH1 and MSH2 loss (P=0.024 and 0.049); No different trend between expression rate of dMMR and proficient mismatch repair (52.6%, 10/19 vs 47.4%, 9/19) in positive PD-L1 stage Ⅱ CRC.

PD-L1 showed the difference expression in dMMR CRC tumor, it was implied that we need to take both dMMR and PD-L1 factors into consideration to screen suitable patients before targeting therapy.