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

BACKGROUND AND OBJECTIVES: The 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.

METHODS: This 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.

RESULTS: PD-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).

CONCLUSIONS: The 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.