The chaperone HSP70 protein is widely present in many different tumors and its expression correlates with an increased cell survival, low differentiation, and poor therapeutic outcome in human breast cancer. The intracellular protein has prevalently a cytoprotective function, while the extracellular HSP70 mediates immunologic responses. Evolutionarily, HSPs are well conserved from prokaryotes to eukaryotes, and human HSP70 shows a strong similarity to that of plant origin. In the current article, we have tested the potential effect of recombinant HSP70, from Arabidopsis thaliana, on cell survival and metastatic properties of breast cancer cells. Our data show that HSP70 sustains cell viability in MCF-7 and MDA-MB-231 breast tumoral cells and increases Cyclin D1 and Survivin expression. The extracellular HSP70 triggers cell migration and the activation of MMPs particularly in MDA-MB-231 cells. Furthermore, under UV-induced stress condition, the low levels of phospho-AKT were increased by exogenous HSP70, together with the upregulation of Cyclin D1, particularly in the tumoral cell phenotype. On the other hand, UV increased TP53 expression, and the coincubation of HSP70 lowers the TP53 levels similar to the control. These findings correlate with the cytoprotective and antiapoptotic role of HSPs, as reported in different cellular contexts. This is the first study on mammary cells that highlights how the heterologous HSP70 from Arabidopsis thaliana sustains cell survival prevalently in breast cancer cell types, thus maintaining their metastatic potential. Therefore, targeting HSP70 would be of clinical importance since HSP70 blocking selectively targets tumor cells, in which it supports cell growth and survival. Mol Cancer Ther; 15(5); 1063-73. ©2016 AACR.