Calreticulin, since its discovery as a ubiquitous protein of endoplasmic reticulum, has become recognized as a multifunctional luminal resident protein affecting many cellular functions ranging from development to death of a cell. However its role in cancer and significance for therapy remains to be clarified. Here to examine its effects, the calreticulin gene was over expressed in MCF-7 human breast cancer cell lines and influence on apoptosis was examined through an MTT assay. Upon culture in a suitable medium, cells transfected with the calreticulin gene were significantly more susceptible to apoptosis compared to controls. These findings therefore render a novel mechanism by which cancerous cells can be triggered to undergo death by upregulation of a protein resident in the lumen of the endoplasmic reticulum.