HOXB9, a gene promoting tumor angiogenesis and proliferation, as a prognostic factor in breast cancer.
33 Background: We demonstrated that HOXB9, a member of homeobox genes, expression promoted tumor neovascularization and metastasis in vitro and in vivo assay. These findings imply that overexpression of HOXB9 contributes to tumor progression through activation of signaling pathways that alter both tumor-specific cell fates and tumor-stromal microenvironment, leading to increased invasion and metastasis. (Hayashida et al., PNAS 2010) We sought to determine whether these results could be extended to the clinical application. In this study, we evaluated the correlation between HOXB9 expression, clinical outcomes, and the clinicopathological variables in breast cancer patients, and the contribution of HOXB9 expression to tumor cell proliferation and angiogenesis. Methods: A consecutive series of 141 patients with invasive ductal carcinoma who underwent surgical treatment were examined. HOXB9 protein expression was analyzed immunohistochemically using the anti-human HOXB9 polyclonal antibody. Immunostaining of Ki-67, CD31, and CD34 were performed to evaluate the association of proliferation and tumor angiogenesis with HOXB9 expression. Results: Of 141 tumor specimens immunostained for HOXB9, 69 specimens (48.9%) were positive staining. Univariate logistic regression revealed ER and PgR negativity, HER2 positivity, high nuclear grade, and large pathological tumor size as significant variables associated with HOXB9 expression. Moreover, 12 (92.3%) out of 13 triple negative breast cancer showed HOXB9 expression. The disease-free survival (DFS) and the overall survival were significantly different between the HOXB9 positive and negative group; HR=20.714, p=0.001, HR 9.206, p=0.003, respectively. A Multivariate analysis indicated that HOXB9 expression was the only independent prognostic factor for DFS (HR=15.532, p=0.009). In subgroup analysis, HOXB9 positive tumors showed a significant increase in the number of vasculature and the Ki-67 ratio in comparison with HOXB9 negative. Conclusions: Our results suggest that HOXB9 expression promoting the tumor proliferation and the angiogenesis is a significant prognostic factor in breast cancer.