PD-L1 expression on tumor cells and tumor infiltrating immune cells in Chinese colorectal cancer patients.

Abstract

e16111 Background: Nowadays, immune checkpoint inhibitors (ICIs) targeting programmed death-1/ligand-1 (PD-1/PD-L1) have been an alternative in cancer treatments. Previous biomarker analysis found that response to anti-PD1/PD-L1 was associated with PD-L1 expression on tumor cells and/or tumor infiltrating immune cells in some cancer types. Explorations of IMblaze370 study demonstrated better survival outcome in colorectal cancer (CRC) patients with positive PD-L1 expression compared with those with negative PD-L1 expression in the atezolizumab group. Our study investigated PD-L1 expression profile in Chinese CRC population. Methods: PD-L1 expression on tumor cells or tumor infiltrating immune cells in 816 CRC tumors between January 01, 2017 and December 02, 2019 in 3D Medicines database was assessed by immunohistochemistry assay (SP263 or 22C3). We defined percentage of PD-L1 expression on tumor cells as tumor proportion score (TPS) strong positive ≥50%, moderate positive ≥5% and < 50%, weak positive ≥1% and < 5%, and negative < 1%. Similarly, we defined percentage of PD-L1 expression on infiltrating immune cells as immune proportion score (IPS) strong positive ≥10%, moderate positive ≥5% and < 10%, weakly positive ≥1% and < 5%, and negative < 1%. In addition, MSI status was evaluated with targeted next-generation sequencing covering 100 MSI loci. Results: 12 (1.5%) individuals had TPS as strong positive, 63 (7.7%) as moderate positive, 95 (11.6%) as weak positive and 646 (79.2%) as negative. Meanwhile, TPS of patients were 55 (6.7%) for strong positive, 49 (6.0%) for moderate positive, 34 (4.2%) for weak positive and 678 (83.0%) for negative, respectively. 16.9% in Chinese CRC patients here were defined as positive PD-L1 expression (IPS ≥1%), which is lower than the positive proportion of CRC in IMblaze370 study (39.9% for IPS ≥1%, P < 0.0001). The PD-L1 expression on tumor cells and on tumor infiltrating immune cells showed minimal overlap. In detail, only 29 (3.6%) patients exhibited simultaneously TPS positive (≥1%) and IPS positive (≥1%). Furthermore, IPS was not associated with MSI status (P = 0.9153), while TPS showed an association with MSI-H (P < 0.0001). In detail, 45.5% of MSI-H CRC patients were TPS positive. Conclusions: Chinese CRC patients express PD-L1 with 20.8% TPS positive and 17.0% IPS positive, and TPS positive were related to MSI-H. When studying the connection between the efficacy of PD1/PD-L1 inhibitors and PD-L1 expression, TPS and IPS detection would be both considered to engage.