To investigate whether anticancer efficacy of GPIbα Ab is associated with the hypoxia, the immunohistochemical staining of hypoxia-inducible factor-1 alpha (HIF1-α) was carried out, and we found that the tumor tissues of Rip1-Tag2 mice treated with GPIbα Ab and RIgG showed high levels of HIF-1α immunoreactivity and there was no difference between GPIbα Ab and RIgG group (Supplemental Figure 6). Here, HIF1A is linked to neoplasm.