Clinical significance of programmed cell death‐ligand 1 expression and the immune microenvironment at the invasive front of colorectal cancers with high microsatellite instability

摘要

Immunotherapy is reportedly effective in colorectal cancers (CRCs) with high microsatellite instability (MSI‐H); however, the specific cell types that respond to immune checkpoint therapy are unclear. Herein, we aimed to examine the expression of programmed cell death‐ligand 1 (PD‐L1) and related proteins in MSI‐H and microsatellite‐stable (MSS) CRCs to investigate the immune microenvironment at the tumor's invasive front. The MSI status was retrospectively assessed in 499 patients undergoing surgical resection of primary CRC; of these, 48 were classified as MSI‐H. Propensity score matching was performed, and tissues from 36 and 37 patients with MSI‐H and MSS CRCs, respectively, were immunohistochemically evaluated for PD‐L1, PD‐1, CD8 and CD68. PD‐L1 expression was evaluated separately for tumor cells (PD‐L1 [T]) and tumor‐infiltrating myeloid cells in the stroma (PD‐L1 [I]). PD‐L1 (T) was positive in only 5.4% and 36.1% of MSS and MSI‐H CRCs, while PD‐L1 (I) was positive in 27% and 72.2% of these CRCs, respectively. The PD‐L1 (T) and PD‐L1 (I) expression levels in MSI‐H CRCs significantly correlated with poor differentiation, lymphatic invasion and vascular invasion ( p ??0.05), and with early‐stage adenocarcinoma and high budding grade ( p ??0.05), respectively. Significantly more PD‐L1 (I), CD8‐positive cells and CD68‐positive macrophages were present at the invasive front than in the central tumor in MSI‐H CRCs ( p ??0.005). PD‐L1 was expressed on both tumor cells and CD68/CD163‐positive (M2) macrophages at the invasive front of MSI‐H CRCs. In conclusion, PD‐L1‐positive tumor cells and M2‐type tumor‐associated macrophages may contribute to tumor invasion and immune escape at the invasive front.