PD-1/PD-L1 expression and tumor-infiltrating lymphocytes are prognostically favorable in advanced high-grade serous ovarian carcinoma

The response rate to checkpoint inhibitors for women with high-grade serous carcinoma of the ovary, fallopian tube, and peritoneum (HGSC) is modest, and development of predictive biomarkers is needed. The main focus has been on tumor cell PD-L1 expression, but its assessment alone is insufficient for patient selection in most malignancies. We mapped the presence of macrophages (CD68 and CD163) and lymphocytes (CD3) located within the tumor epithelium, the cell type-specific expression of PD-L1 and PD-1, and their impact on 5-year overall survival (OS) in a consecutive cohort of 130 women diagnosed with advanced HGSC between 2011 and 2015. PD-L1 was expressed mainly by macrophages (not by tumor cells) and PD-1 by lymphocytes. Women with higher CD3, PD-L1, and PD-1 expression had improved OS (P = 0.03, P = 0.007, and P = 0.02, respectively). In the external data set (203 women), high expression of CD274 (encoding PD-L1) was associated with improved OS (P = 0.03), in accordance with our results. Furthermore, higher CD163 expression was associated with better outcome in women with no residual tumor after primary surgery (P = 0.02). Thus, women with greater lymphocyte tumor infiltration had better outcome and PD-L1/PD-1 expression, regardless of PD-1/PD-L1 being markers for immune suppressive pathways, conferred a survival benefit in our cohort. Our results highlight that tumor immunity may be harnessed in subsets of HGSC.