HIF1A Overexpression Is Associated with Poor Prognosis in a Cohort of 731 Colorectal Cancers

Tissue hypoxia commonly occurs in tumors. Hypoxia- inducible factor (HIF)-1 and HIF-2, which are essential mediators of cellular response to hypoxia, regulate gene expression for tumor angiogenesis, glucose metabolism, and resistance to oxidative stress. Their key regulatory subunits, HIF1A (HIF-1α) and endothelial PAS domain protein 1 (EPAS1; HIF-2α), are overexpressed and associated with patient prognosis in a variety of cancers. However, prognostic or molecular features of colon cancer with HIF expression remain uncertain. Among 731 colorectal cancers in two prospective cohort studies, 142 (19%) tumors showed HIF1A overexpression, and 322 (46%) showed EPAS1 overexpression by immunohistochemistry. HIF1A overexpression was significantly associated with higher colorectal cancer-specific mortality in Kaplan-Meier analysis (log-rank test, P < 0.0001), univariate Cox regression (hazard ratio = 1.84; 95% confidence interval, 1.37 to 2.47; P < 0.0001) and multivariate analysis (adjusted hazard ratio = 1.72; 95% confidence interval, 1.26 to 2.36; P = 0.0007) that adjusted for clinical and tumoral features, including microsatellite instability, TP53 (p53), PTGS2 (cyclooxygenase-2), CpG island methylator phenotype, and KRAS, BRAF, PIK3CA, and LINE-1 methylation. In contrast, EPAS1 expression was not significantly associated with patient survival. In addition, HIF1A expression was independently associated with PTGS2 expression (P = 0.0035), CpG island methylator phenotype-high (P = 0.013), and LINE-1 hypomethylation (P = 0.017). EPAS1 expression was inversely associated with high tumor grade (P = 0.0017) and obesity (body mass index ≥ 30 kg/m²) (P = 0.039). In conclusion, HIF1A expression is independently associated with poor prognosis in colorectal cancer, suggesting HIF1A as a biomarker with potentially important therapeutic implications.Tissue hypoxia commonly occurs in tumor, and adaptation to tissue hypoxia appears to be one of important characteristics of malignant cells.^1,2 Hypoxia-inducible factor (HIF)-1 and HIF-2 play a key role in cellular adaptation to hypoxia and regulate the expression of genes responsible for glucose metabolism, angiogenesis, and cell survival.^1,2,3 Thus, HIF and related pathways are potential therapeutic targets.^4,5 Cellular HIF levels are regulated not only by the oxygen-dependent pathway (eg, VHL and prolyl hydroxylase, EGLN) but also by the oxygen-independent pathway (eg, glycogen synthase kinase 3, the phosphatidylinositol 3-kinase pathway, the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathway).^6,7 HIF and hypoxia signaling influence a wide variety of pathways including those related to vascular endothelial growth factor (VEGF), cyclins, and MTOR.^1,2 Thus, cellular HIF levels may modify responsiveness to drugs targeting those pathways or hypoxia signaling, and it is of particular interest to examine HIF expression in human cancers. Key regulatory subunits of HIF, HIF1A (the official symbol for HIF-1α), and endothelial PAS domain protein 1 (EPAS1; the official symbol for HIF-2α) are differentially overexpressed^8,9 and have distinct functions in human cancers.^9,10,11 HIF1A expression leads to increased tumor growth and metastasis in some studies,^12,13,14,15 whereas HIF1A inhibits tumor growth by cell cycle arrest or apoptosis induction in other studies.^16,17,18,19 Similar paradoxical effects of EPAS1 have also been reported; EPAS1 appears to promote cancer development and progression in neuroblastoma and renal carcinoma,^20,21,22 whereas it appears to inhibit tumor growth in other cancers including colon cancer.^23,24,25Previous data on HIF1A, EPAS1, and clinical outcome in colorectal cancer have been inconclusive. A study of 90 rectal cancer patients showed poor prognosis associated with HIF1A but not with EPAS1.²⁶ In contrast, another study of 87 colorectal cancer patients reported poor prognosis associated with EPAS1 but not with HIF1A.²⁷ Among studies assessing only HIF1A, some reported its independent prognostic effect^28,29 whereas others did not.^30,31 However, all previous studies^{26,27,28,29,30,31} were limited by small sample sizes (N <136). Considering the increasing importance of the HIF pathway as a potential target for cancer treatment,^1,2,6 the assessment of HIF1A and EPAS1 expression and clinical outcome using a large number of colorectal cancers is needed.We therefore examined prognostic effects of HIF1A and EPAS1 expression among 731 colorectal cancer patients identified in two prospective cohort studies. Moreover, because we concurrently assessed other important molecular events including mutations in KRAS, BRAF, and PIK3CA, LINE-1 hypomethylation, microsatellite instability (MSI), and the CpG island methylator phenotype (CIMP), we could evaluate the effect of HIF1A or EPAS1 expression after controlling for these potential confounders.