Programmed cell death ligand 1 (PD-L1, CD274) in cholangiocarcinoma - correlation with clinicopathological data and comparison of antibodies

Abstract

Background: Cholangiocarcinoma (CCA) may arise in the intra- or extrahepatic biliary tract and is associated with a poor prognosis. Despite recent advances, to date there is still no established targeted therapeutic approach available. Non-surgical therapeutic agents are urgently needed, as most patients are non-eligible to surgical resection. Anti-PD-L1 therapy prevents cancer cells from evading the immune system and has emerged as a new treatment option in several cancer entities. Recently, PD-L1 expression has been analyzed in comparably small CCA patient cohorts. However, a systematic validation of different PD-L1 antibodies has not been performed in CCA so far.

Methods: We stained a tissue microarray consisting of 170 patients, including 72 intrahepatic cholangiocarcinomas (iCCAs), 57 perihilar cholangiocarcinomas (pCCAs) and 41 distal cholangiocarcinomas (dCCAs) by immunohistochemistry and evaluated PD-L1 positivity in tumor and stromal cells. We analyzed three different PD-L1 antibodies (clones 28-8, SP142, and SP263) that are frequently used and recommended for predictive diagnostic testing in other cancer types.

Results: For PD-L1 antibody clone SP263, 5% of iCCAs, 4% of pCCAs and 3% of dCCAs exhibited PD-L1 expression on tumor cells, thereby showing the highest frequencies of PD-L1 positivity. Accordingly, highest PD-L1 positivity rates of stromal cells with 31% in iCCA, 40% in pCCA and 61% in dCCA were detected for clone SP263. Agreement of PD-L1 positivity in tumor cells was moderate for clone 28-8 and SP263 (κ = 0.44) and poor between 28-8 and SP142 (κ = 0.13), as well as SP142 and SP263 (κ = 0.11), respectively. Statistical analyses of PD-L1 expression (clone SP263) on tumor cells with clinicopathological data revealed a positive correlation with shortened overall survival in CCA patients.

Conclusions: Selection of appropriate PD-L1 antibodies and careful evaluation of immunohistochemical staining patterns have a significant impact on PD-L1 testing in CCA. Clinical trials are necessary to investigate the putative beneficial effects of PD-L1 targeted immunotherapy in CCA patients.

Keywords: 28–8; CD274; Cholangiocarcinoma; PD-L1; SP142; SP263.

Fig. 1

Examples of PD-L1 staining in a representative intrahepatic cholangiocarcinoma. The different staining characteristics of PD-L1 clones 28–8, SP142 and SP263 are displayed. In the first row, tumor cells show membranous positivity of few tumor cells with antibody clones 28–8 (a) and SP263 (c), but not with clone SP142 (b). In the second row, stromal inflammatory cells show membranous PD-L1 expression with all three antibody clones (d-f), while tumor cells are negative. In the third row, all samples are negative, both in tumor and stromal cells, and with all three PD-L1 antibodies (g-i). Original magnification: 200x, PD-L1 positive tumor cells are highlighted by black arrows, PD-L1 positive stromal cells are highlighted by black triangles

Fig. 2

PD-L1 status in correlation with overall survival in cholangiocarcinoma patients. PD-L1 immunohistochemistry results using clone SP263 were correlated with overall survival of CCA patients. Kaplan-Meier curves show a trend of decreased overall survival in CCA patients with any PD-L1 positivity in tumor cells (p = 0.09; a). Significant decreased overall survival rates are seen in CCA patients with PD-L1 positivity in > 5% of tumor cells (p < 0.001; b). PD-L1 positivity in stromal cells has no impact on overall survival of CCA patients in none vs any (p = 0.89; c) or testing the cut-off of 5% (p = 0.69; d)

Fig. 3

PD-L1 status in correlation with patient overall survival in cholangiocarcinoma subtypes. PD-L1 immunohistochemistry (clone SP263) results are correlated with overall survival of CCA patients, stratified by CCA subtypes. In intrahepatic CCA (iCCA), Kaplan-Meier curves show no significant overall patient survival difference in correlation with none vs any PD-L1 positivity in tumor cells (a), while significant decreased overall survival rates are seen in iCCA patients with PD-L1 positivity in > 5% of tumor cells (p = 0.024); (b)). In perihilar CCA (pCCA), Kaplan-Meier curves show no significant overall patient survival difference in correlation with none vs any PD-L1 positivity in tumor cells (c), while by trend decreased overall survival rates are in pCCA patients with PD-L1 positivity in > 5% of tumor cells (p = 0.060; (d)). PD-L1 positivity in distal CCA (dCCA) has no impact on overall patient survival in none vs any (e) or testing the cut-off of 5% (f)