Differences in PD-L1 expression on tumor and immune cells between lung metastases and corresponding primary tumors

It has been reported that the tumor microenvironment, including tumor-associated immune cells (ICs) and programmed cell death-ligand 1 (PD-L1) expression, differs between primary and metastatic tumors. This study aimed to elucidate the differences in PD-L1 expression on tumor cells (TCs) and ICs between lung metastases and corresponding primary tumors. We analyzed paired lesions from 44 patients diagnosed with lung metastases between 2005 and 2017 at Kyushu University. The percentages of PD-L1-positive TCs and ICs in lung metastases and the primary tumor were classified into five categories (0: