Abstract 2989: Expression of immune checkpoints proteins and their prognostic relevance in prostate cancer

Abstract

Abstract Immune checkpoint proteins including programmed death ligand 1, 2 (PD-L1, PD-L2) and B7-H3 play important roles for immune evasion in many cancer types. PD-L1 is an established therapeutic target in lung cancer and in a growing number of other indications. The clinical success of PD-L1 inhibitors has accelerated the development of drugs also targeting PD-L2 and B7-H3. In prostate cancer, studies on the prevalence and clinical relevance of these proteins have been inconclusive. Here, we performed immunohistochemical analysis of PD-L1, PD-L2 and B7-H3 in our large prostate cancer prognosis tissue microarray (TMA) containing tissue samples from more than 17,000 patients. Normal prostate glands were negative for PD-L1 and B7-H3, but positive for PD-L2. We found that 47% of 12,808 interpretable cancers showed B7-H3 expression, and 92% of 9,463 cancers showed PD-L2 expression, while expression of PD-L1 was virtually absent (0.2% of 17,392 tumors) in epithelial cells. Stroma cells and immune cells were entirely negative for PD-L1 and B7-H3, while some faint staining of lymphocytes was occasionally observed for PD-L2. In cancers, PD-L2 and B7-H3 staining had different prognostic impact, which depended on the ERG status: B7-H3 expression was linked to young patient age, advanced stage, high Gleason grade, lymph node metastasis (p<0.0001 each), presence of PTEN deletion (p<0.0001), and poor prognosis in ERG negative cancers (p<0.0001), while PD-L2 expression was linked to beneficial tumor features and good prognosis exclusively in tumors with ERG fusion (p<0.0001). In a multivariate analysis including pT stage, Gleason grade, nodal stage, resection margin and preoperative PSA level, B7-H3 expression was an independent prognostic factor (p=0.0004). In summary, the results of our study identify a subset of young patients with ERG negative aggressive prostate cancers that might benefit from anti-B7-H3 therapy in the future. PD-L2 expression appears to protect tumors from progression and does not seem to be suitable as a potential target in prostate cancer. PD-L1 expression is extremely rare in this disease, suggesting that only few prostate cancer patients might benefit from PD-L1 inhibitors. Citation Format: Claudia Hube-Magg, Cornelia Schroeder, Ronald Simon, Martina Kluth, Till Krech, Franziska Büscheck, Frank Jacobsen, Doris Höflmayer, Lars Budäus, Hartwig Huland, Markus Graefen, Guido Sauter, Thorsten Schlomm. Expression of immune checkpoints proteins and their prognostic relevance in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2989. doi:10.1158/1538-7445.AM2017-2989