This would imply that GSK3β inhibition could reverse the negative effect of prolonged hypoxia on HIF-1α accumulation; however, these effects may be cell type specific since the hypoxia effects on GSK3β phosphorylation were not observed in other cell types including some different breast cancer cell lines (Blancher et al., 2000), PC-3 prostate cancer cells (Zhong et al., 2000), and 3T3 cells (Laughner et al., 2001). This evidence concerns the gene HIF1A and breast cancer.