P2.04-020 Expression Patterns and Prognostic Value of PD-L1 and PD-1 in Thymoma and Thymic Carcinoma: Topic: Thymic Malignancies Clinical and Translational

Abstract

Thymic epithelial tumors (TETs) including thymoma (TA) and thymic carcinoma (TC) are rare, and little data are available to guide treatment. As the thymus plays a critical role in immune homeostasis, immunotherapy with checkpoint blockade is an attractive treatment strategy for patients with TET. Published data regarding the expression patterns and prognostic implications of PD-L1 expression in TET have yielded conflicting results, and have included limited data regarding PD-1 expression. A retrospective review was carried out at Ohio State University of 35 pts with TET, with tumor specimens available at our institution from 2000 – 2010. PD-1 and PD-L1 expression was assessed by immunohistochemistry on tumor samples (utilizing PD-1 clone: NAT105 and PD-L1 clone:22C3 antibodies), and graded 0-5 according to expression (0 – no expression, 5 – high expression). Clinicopathologic characteristics assessed included age, grade, stage, overall survival, smoking status, and diagnosis of myasthenia gravis. PD-1 and PD-L1 expression were assessed in 35 pts, including 32 pts with thymoma and 3 pts with thymic carcinoma. PD-L1 expression was detected in 83% (29/35) tumor samples, including 100% (3/3) of thymic carcinoma pts and 81% (26/32) of thymoma pts. PD-1 expression was detected in 77% (27/35) of samples, including 33% (1/3) of thymic carcinoma pts and 81% (26/32) thymoma pts. High levels (IHC >/= 3) of PD-L1 were detected in 57% (20/35) of pts, and high levels of PD-1 expression (IHC >/= 3) were detected in 31% (11/35) pts. A nonsignificant trend towards poorer overall survival was seen in patients with PD-L1 expression (p=0.097, log-rank test). Unlike prior studies, PD-L1 expression was not associated with higher grade tumors (B2, B3, C) or higher stage at diagnosis. Interestingly, high PD-1 expression was significantly associated with lower grade tumors (p = 0.031), but not overall survival. Expression of PD-L1 and PD-1 was not significantly associated with stage at diagnosis, smoking, recurrence, or diagnosis of myasthenia gravis. This study confirms high expression of PD-L1 and PD-1 in TETs, including thymoma and thymic carcinoma. PD-L1 expression was associated with a trend towards shorter overall survival. The high proportion of patients with high PD-L1 and PD-1 expression supports the use of anti PD-1 therapies in this patient population, and prospective trials are needed to assess PD-L1 and PD-1 as predictive and prognostic biomarkers in TET.