A comparative study of PD-L1 immunohistochemical assays with four reliable antibodies in thymic carcinoma

// Tadashi Sakane 1, * , Takayuki Murase 2, * , Katsuhiro Okuda 1 , Hisashi Takino 2 , Ayako Masaki 2 , Risa Oda 1 , Takuya Watanabe 1 , Osamu Kawano 1 , Hiroshi Haneda 1 , Satoru Moriyama 1 , Yushi Saito 3 , Takeshi Yamada 4 , Ryoichi Nakanishi 1 and Hiroshi Inagaki 2 1 Department of Oncology, Immunology and Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan 2 Department of Pathology and Molecular Diagnostics, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan 3 Department of Chest Surgery, Toyota Memorial Hospital, Toyota 471-8513, Japan 4 Department of Thoracic Surgery, Kariya Toyota General Hospital, Kariya 448-8505, Japan * These authors contributed equally to this work Correspondence to: Katsuhiro Okuda, email: kokuda@med.nagoya-cu.ac.jp Keywords: programmed death 1 (PD-1); programmed death ligand 1 (PD-L1); thymic carcinoma; squamous cell carcinoma; immunohistochemistry Received: September 15, 2017      Accepted: January 02, 2018      Published: January 08, 2018 ABSTRACT Currently, four immunohistochemical assays are registered with the US Food and Drug Administration to detect the expression of PD-L1. We investigated the PD-L1 expression in thymic carcinomas using these four diagnostic assays. The cases of 53 patients were reviewed and their specimens were subjected to four PD-L1 assays with different antibodies (SP142, SP263, 22C3, and 28-8). The PD-L1 expression in tumor cells (TCs) and immune cells (ICs) was evaluated. In TCs, the four assays showed similar scores in each case. Histopathologically, high TC scores were observed in squamous cell carcinomas (SqCCs). Meanwhile, there were no significant relationships among the IC scores in the four assays. In SqCCs, the high expression of PD-L1 (defined as ≥50% TC score) in TCs tended to be associated with early stage cancer. The patients with high expression levels of PD-L1 tended to show longer overall survival in the 22C3 assays (p=0.0200). In thymic carcinomas, the staining pattern showed high concordance among the four assays when TCs – rather than ICs – were stained. High PD-L1 positivity in TCs, especially in SqCCs, indicated that PD-1/PD-L1 targeted therapy may be a promising therapeutic approach.