Cancer activation pathways of thymic epithelial tumors (TETs) by targeted gene expression analysis.

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8575 Background: TETs are rare malignancies of the anterior mediastinum. Clinical behavior varies from mild thymoma (T) A to aggressive thymic carcinoma (TC). The biology of TETs is poorly understood and knowledge of the transcriptomic fingerprint of T and TC is limited. Additionally, up to 30% of patients (pts) will develop associated autoimmune disorders (AIDs). We aimed to characterize the main cancer activation pathways of the TET subgroups. Methods: We selected a representative balanced set of Ts and TCs to analyze 24 main cancer activation pathways using HTG Oncology biomarkers panel (2562 genes) by RNA sequencing. Tumor representative paraffin-embedded blocks were macrodissected for gene expression analysis. We analyzed epidemiologic, clinical and pathological characteristics of pts with TET’s and correlated with genes expression based on cancer Hallmarks. Results: From January 2010 to December 2019, 219 pts were included in the cohort. Molecular results of 194 pts were available. Median age at diagnosis was 56 (9-83) years. 54.1% were women. 65/194 (33.5%) reported AIDs. T B2 was the most frequent (n=41, 21.1%), followed by B1, AB, B3, TC and A. RNA expression analysis identified 2 main clusters, corresponding mainly to T (cluster 2) and TC (cluster 1) respectively (p<0.0001) (Table). Tumors of cluster 1 (TCs predominant) shown activated pathways (MYC [gene ratio= 0.5]; p<0.0001). In cluster 2 (T predominant), activated pathways differed among subgroups: B1 (E2F[0.5], G2M checkpoint [0.45]; p<0.001), B2 (E2F [>0.4]; p<0.0001). Routes were mostly suppressed: A (MYC [>0.5], E2F[>0.4], G2M checkpoint[>0.45], mitotic spindle[>0.35], MTOR [<0.35]; p<0.001), AB (INFα [>0.5], inflammatory response [>0.45], INTɣ [0.45], NFkb [>0.4], MTOR[>0.4]; p<0.001), B1 (EMT [0.6], angiogenesis [>0.5], INFα [0.5], homeostasis [0.5], NFkb [0.5], INTɣ [>0.45], myogenesis [<0.4]; p<0.0001), B2 (INFα [>0.65], INTɣ [>0.5], NFkb [0.5], EMT [0.45], inflammatory response [<0.4]; p< 0.0001), B3 (EMT [0.6], MYC [0.45]; p<0.001). Among pts reporting AIDs 61 and 4 were associated to cluster 2 and 1, respectively (p=0.017). Conclusions: We describe differential molecular characteristics among histological subgroups in 2 clusters. The analysis suggests new therapeutic venues. Additional analysis will be presented on outliers and response to treatment.[Table: see text]