Immunohistochemistry and oxygen saturation endoscopic imaging reveal hypoxia in submucosal invasive esophageal squamous cell carcinoma

BACKGROUND: Hypoxic microenvironment is prominent in advanced esophageal squamous cell carcinoma (ESCC). However, it is unclear whether ESCC becomes hypoxic when it remains in the mucosal layer or as it invades the submucosal layer. We aimed to investigate whether intramucosal (Tis‐T1a) or submucosal invasive (T1b) ESCC becomes hypoxic using endoscopic submucosal dissection samples. METHODS: We evaluated the expression of hypoxia markers including hypoxia inducible factor 1α (HIF‐1α), carbonic anhydrase IX (CAIX), and glucose transporter 1 (GLUT1) by H‐score and vessel density by microvessel count (MVC) and microvessel density (MVD) for CD31 and α‐smooth muscle actin (α‐SMA) with immunohistochemical staining (n = 109). Further, we quantified oxygen saturation (StO(2)) with oxygen saturation endoscopic imaging (OXEI) (n = 16) and compared them to non‐neoplasia controls, Tis‐T1a, and T1b. RESULTS: In Tis‐T1a, cccIX (13.0 vs. 0.290, p < 0.001) and GLUT1 (199 vs. 37.6, p < 0.001) were significantly increased. Similarly, median MVC (22.7/mm(2) vs. 14.2/mm(2), p < 0.001) and MVD (0.991% vs. 0.478%, p < 0.001) were markedly augmented. Additionally, in T1b, the mean expression of HIF‐1α (16.0 vs. 4.95, p < 0.001), CAIX (15.7 vs. 0.290, p < 0.001), and GLUT1 (177 vs. 37.6, p < 0.001) were significantly heightened, and median MVC (24.8/mm(2) vs. 14.2/mm(2), p < 0.001) and MVD (1.51% vs. 0.478%, p < 0.001) were markedly higher. Furthermore, OXEI revealed that median StO(2) was significantly lower in T1b than in non‐neoplasia (54% vs. 61.5%, p = 0.00131) and tended to be lower in T1b than in Tis‐T1a (54% vs. 62%, p = 0.0606). CONCLUSION: These results suggest that ESCC becomes hypoxic even at an early stage, and is especially prominent in T1b.