P2.01-056 Distinct PD-L1 Expression in Different Components of Pulmonary Sarcomatoid Carcinoma and Its Association with MET Mutation: Topic: Immune Mechanisms in Thoracic Cancer and Targeted Therapy

Pulmonary Sarcomatoid Carcinoma (PSC) is a unique and highly aggressive subtype of non-small cell lung cancer (NSCLC), characterized by a component of sarcoma or sarcoma-like differentiation. It is generally resistant to platinum-based chemotherapy. However, frequent KRAS and the MET exon 14 skipping mutations have been reported in this subtype. Recently, immunotherapy with antibodies against PD-1/PD-L1 has led to clinical benefits in managing NSCLC. Immune biomarker expression of PD-L1 in differential components of PSC and its relationship with other molecular markers has not been defined and thus there is critical need to investigate its expression profile in this deadly disease. We investigated PD-L1 expression by immunohistochemistry (IHC) using tissue microarrays from a cohort of 41 patients with PSC (antibody: PD-L1/CD274 (SP142)). Positive cases were defined as PD-L1 ≥ 1%. The clinical and molecular characterization of these cases was previously reported (PMID: 26215952). Among the 41 cases, 36 had sufficient tumor tissue for PD-L1 assessment, 8 (20%) were identified with MET exon 14 skipping mutation and 6 (15%) were found to have KRAS mutations. The PD-L1 expression was positive in 75% (27/36) of cases. Among the positive cases, 78% expressed PD-L1 ≥ 50%, whereas 22% had PD-L1 staining of 1-49%. Interestingly, only 33% (9/27) had PD-L1 expression in both epithelial and sarcomatoid components, whereas the remaining 66% detected PD-L1 in just one component. The PD-L1 expression was statistically different between the two components (P=0.007). Moreover, all 8 patients with MET exon 14 skipping mutation were PD-L1 positive (6 with PD-L1 ≥ 50%), whereas 5 of 6 patients with KRAS mutation expressed PD-L1 (2 with PD-L1 ≥ 50%). The average age at diagnosis was similar between the PD-L1 positive vs. negative groups (71 years). There was a trend of shorter overall survival in patients whose tumors were positive for PD-L1 (671 vs. 985 days). In our particular cohort of PSC patients, high PD-L1 (≥ 50%) was expressed in the large majority of cases which favors potential application of immunotherapy in this disease. In addition, it appears that the expression of PD-L1 is different in the epithelial and sarcomatoid components which could affect scoring in practice. Furthermore, the overall positivity of PD-L1 expression in the unique molecular subtype of PSC patients with MET exon 14 skipping mutation indicates potential interplay between the two biomarkers and suggests that exploration of combination MET and immunotherapy in this subtype is warranted.