Neuroendocrine carcinoma of the esophagus: A genomic landscape study.

642 Background: Esophageal neuroendocrine carcinoma (ENEC) is a rare and aggressive upper GI tract malignancy when compared with the far more frequent esophageal adenocarcinoma (EAC). Methods: 194 ENEC and 9920 EAC underwent hybrid capture based comprehensive genomic profiling (CGP) to identify all classes of genomic alterations (GA). Microsatellite instability status (MSI) and tumor mutation burden (TMB) were determined from the sequencing data. PD-L1 expression was determined by IHC using the Dako TPS score (0% = negative; 1-49% = low positive and >50% = high positive). Results: Although the mean (63.6 vs 64.8 yrs) and median (65 yrs for both) ages of the 2 groups were nearly identical, the ENEC group featured significantly more female patients (20.6% vs 13.2%; p=.002). The number of driver GA per tumor sample was slightly higher in the EAC group (NS). MSI-High status was infrequent in both groups (2.1% vs 2.6%; NS), the relative low median and mean TMBs were also similar with the TMB >10, % frequency slightly lower in the ENEC group (7.2% vs 8.4%; NS) and low PD-L1 expression was higher in the ENEC group but low sample numbers impacted significance (25.0% vs 12.3%; NS). Both ENEC and EAC featured high frequencies of GA in TP53 (84.5% vs 86.9%; NS) with additional GA in RB1 relatively unique for the ENEC (40.2% vs 1.9%; p