Programmed Death Ligand 1 and Immune Cell Infiltrates in Solitary Fibrous Tumors of the Pleura

Abstract Background Approximately 10-15% of patients with solitary fibrous tumors of the pleura (SFTP) recur after resection. Many are not candidates for re-resection and lack effective treatments. We explored the expression of PD-L1 as a biomarker for candidacy for treatment with immune checkpoint inhibitors. Methods Review of medical records of 52 patients with primary SFTP, and 5 patients with recurrent SFTP. Immunohistochemistry on tumor tissue was performed to determine the expression of PD-L1 and infiltration by CD8+ immune cells. Results Any PD-L1 expression was observed in 11 (21.2%) primary SFTP. Overall, PD-L1 expression level was 1% in one (1.9%). Tumor infiltration by CD8+ immune cells was absent/rare in 13 (25%) cases, Conclusions A small subset of SFTPs express PD-L1 at low levels (