The aim of this study was (i) to investigate the effect of hypoxia on apoptosis induced by two chemotherapeutic agents in human breast cancer MDA-MB-231 cell line and (ii) to characterize the mechanisms underlying the hypoxia resistance against paclitaxel-induced apoptosis observed in these cells by investigating the putative implication of the two transcription factors HIF-1 and AP1. Here, HIF1A is linked to breast cancer.