Abstract 6143: Tumor immune microenvironment in salivary gland cancer

Abstract

Abstract Purpose/Objectives: Salivary gland cancer (SGC) is a rare malignancy with various pathological types. Although immune checkpoint inhibitors for SGC have been investigated in clinical trials, details of the tumor immune microenvironment (TIME) in SGC remain unclear. The aim of this study was to elucidate the TIME of SGC. Materials/Methods: We selected five typical pathological types of SGC, namely adenoid cystic carcinoma (ACC); adenocarcinoma, not otherwise specified (ANOS); salivary duct carcinoma (SDC); and low/high-grade mucoepidermoid carcinoma (MEC low/high). We investigated the TIME as well as the tumor mutation burden (TMB) of each pathological type in surgical archival tissues obtained from 1999 to 2017 (7 patients in each type, stage III/IVA/IVB [UICC 8th]). TIME was evaluated by multiplexed immunofluorescent staining, including CD3, CD4, CD8, Foxp3, CD204, PD-1, PD-L1, and PD-L2. Tumors with > 1% tumor cells expressing PD-L1 were considered positive for PD-L1. TMB was measured by the Oncomine Tumor Mutation Load Assay, and a high TMB was defined by 10 or more mutations/Mb. Correlation analyses were performed using Pearson’s product moment correlation coefficient. Results: Multiplexed immunofluorescent staining was performed in all 35 archival tissues. ACC showed the lowest infiltration of immune effector cells (ICeff) and suppressor cells (ICsup) in both the tumor and stroma, and a low proportion of cases was positive for PD-L1 (14%). Compared with ACC, MEC high showed higher infiltration of ICeff and ICsup in both the tumor and stroma, and a higher proportion of cases was positive for PD-L1 (71%). Although ANOS, SDC, and MEC low showed modest infiltration of ICeff in the tumor, these subtypes showed higher infiltration of ICeff in the stroma than ACC. TMB was measured in 29 samples; the proportion of TMB high was lower in ACC (33%) and MEC low (0%) than in the other pathological types (ANOS/SDC/MEC high: 60/67/57%). Regarding multiplexed immunofluorescent staining, correlation analysis showed a positive correlation between TMB and CD3+CD8+ T cells in the tumor (r=0.647, P<0.0001). In addition, CD3+CD8+ T cells in the tumor showed a positive correlation with PD-L1 expression in tumor cells (r=0.513, P=0.002) and with CD3+CD4+Foxp3+ T cells in the tumor (r=0.399, P=0.018). However, no correlation was seen between CD3+CD8+ T cells and CD204+ cells in the tumor (r=-0.049, P=0.779). Conclusion: ACC showed less PD-L1 expression in tumor cells and the lowest infiltration of immune cells in both the tumor and stroma compared with other pathological types. These results suggest that the TIME of ACC is the so-called immune desert type, which may in turn explain the mechanisms of the poor response to immune check point inhibitors seen in clinical trials. Citation Format: Yoshiaki Nagatani, Naomi Kiyota, Yoshinori Imamura, Taiji Koyama, Yohei Funakoshi, Masato Komatsu, Masanori Teshima, Ken-Ichi Nibu, Kazuko Sakai, Kazuto Nishio, Manami Shimomura, Tetsuya Nakatsura, Daiki Ikarashi, Takayuki Nakayama, Shigehisa Kitano, Hironobu Minami. Tumor immune microenvironment in salivary gland cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6143.