Grp94 plays an essential role in protein assembly. We previously suggested that Grp94 overexpression is involved in tumor aggressiveness. However, the underlying mechanisms remain unknown. Since many tumors display high Grp94 levels, we investigated the effects of tumor microenvironment on the regulation of this chaperone expression. First, we found out that hypoxia did not change Grp94 expression in the human tumor cell lines MCF-7 (breast cancer) and HepG2 (liver cancer). Second, glucose deprivation significantly increased Grp94 protein levels. Subsequently, we focused in the putative role of Grp94 in the acquisition of an aggressive phenotype by cancer cells. Using a more aggressive cancer cell model (MDA-MB-231 breast tumor cells), we found out that Grp94 knockdown using siRNA decreased the invasive capacity of cancer cells. Moreover, cells with decreased Grp94 levels displayed an enhanced sensitivity of tumor cells to doxorubicin, a standard drug in the treatment of breast cancer. Taken together, our results suggest that the expression of Grp94 is linked to tumor aggressiveness. Therefore, targeting Grp94 could be an effective way to inhibit tumor growth improving chemotherapy outcome.