In particular, hypoxia promotes chemoresistance by enhancing MDR1 expression in tumor cells [28]; for instance, Xie et al. reported a correlation of HIF1α expression and MDR1/Pgp expression in laryngeal cancer Hep 2 cells [28], while Ding et al. described this association in colon carcinoma [29]. This evidence concerns the gene PGP and colon carcinoma.