A significant increase in the number of PD-L1 positive cells indicates that combination treatment may recruit myeloid cells into tumor sites to counterbalance the therapeutic efficacy, which provides the possibility to strengthen the anticancer effect of combining MK1775 and anti-PD-L1 by targeting myeloid cells in the microenvironment of MUS81 deficient gastric cancer. Here, MUS81 is linked to gastric cancer.