The tetraspan protein EMP2 is a novel biomarker for endometrial cancer prognosis and survival. Specificially, in this resubmission, we show that EMP2 expression is upregulated in a significant subset of endometrial hyperplasia and cancer patients. We therefore reasoned that EMP2 may be an effective therapeutic and/or diagnostic target in these populations. To this end, we have developed recombinant antibodies (diabody, minibody, native IgG1) specific for epithelial membrane protein-2 (EMP2). Strikingly, recombinant EMP2 diabodies exhibit strong intrinsic anti-proliferative/pro-apoptotic activity against endometrial cell lines. Moreover, preliminary experiments suggest that recombinant EMP2 diabodies reduce tumor load in vivo, and importantly do not exhibit toxicity against endogenous tissue. Thus, we hypothesize that anti-EMP2 antibodies can be used to target endometrial tumors for diagnostic and therapeutic purposes. In this proposal, we define the effect of recombinant EMP2 antibodies on both proliferation and apoptosis;and, define the mechanism responsible for these effects. In addition, we will utilize micro-PET to visualize and optimize recombinant EMP2 antibody targeting of tumor and non-tumor compartments in vivo. Thus, the proposed experiments will result in a better understanding of the mechanism of EMP2 in endometrial cancer and will provide preclinical evidence on its use in the treatment and diagnosis of disease. We anticipate that the utility of this novel treatment may eventually be pertinent to other EMP2-overexpressing cancer, including breast, ovarian, and primary CNS malignancies. PUBLIC HEALTH RELEVANCE: The tetraspan protein EMP2 is a novel biomarker that appears to be dysregulated in a number of cancers, including endometrial, ovarian, breast, and primary CNS malignancies, and its expression correlates with poor survival rates in some of the tumors. To this end, we propose utilizing recombinant EMP2 antibodies in targeting endometrial cancer cells as a therapeutic agent. If successful, our results may provide pre-clinical evidence as to the efficacy of targeting EMP2 in cancer, and offer new therapeutic alternatives in treatment of these tumors.