The etoposide-induced 24 (EI24) protein is an immediate-early induction target of p53-mediated apoptosis and functions as a tumor suppressor. EI24 contains six transmembrane domains and is localized to the endoplasmic reticulum (ER). It binds to Bcl-2 and may contribute to apoptosis by modulating the activity and function of Bcl-2. EI24 is highly mutated in aggressive breast cancers and its loss in breast cancer tissue correlates with tumor invasiveness. Similar findings in invasive cervical carcinoma suggest that EI24 may be a promising therapeutic target in the treatment of invasive cancer.