Transition of the programmed death 1 pathway from the primary colorectal cancer to its corresponding pulmonary metastasis

Background and ObjectivesThe inhibition of the programmed death 1 (PD-1)/its ligand 1 (PD-L1) pathway may be associated with clinical responses in colorectal cancer (CRC). We aimed to characterize the transition of PD-1/PD-L1 expression through pulmonary metastasis (PM) and its clinical relevance. MethodsThis study retrospectively reviewed 50 patients who had curative resection of primary CRC and its PM. We evaluated the presence of PD-1+ tumor-infiltrating lymphocytes (TILs) and PD-L1+ tumor cells in both the primary tumor and its PM by immunohistochemistry. ResultsPD-L1 was expressed 34.0% of primary lesions and in 38.0% of their PM. A discrepancy in PD-L1 expression between the primary site and its PM was found in 34.0% of our patients. The presence of PD-1+ TILs in the PM was significantly associated with that in its corresponding primary lesion (P=0.003). The longer interval between the primary site and its PM was statistically significant in predicting higher expression of PD-L1 in the PM (P=0.010). ConclusionsThe discordance of PD-L1 expression between the primary tumor and its PM was found in one-third of our patients with CRC. Temporally distant PM from CRC could be associated with the positive expression of PD-L1 in the PM.