Abstract We identified 89 novel candidate markers for prevalent cancers by a systematic Tissue microarray analysis (TMA) of a large collection of polyclonal antibodies (approximately 1600) raised against membrane-associated and secreted human proteins currently marginally characterized. Among them, here we report a novel cancer-associated protein, referred as EXN32, so far only marginally characterized. EXN32 is a metallo-protease highly conserved across species, known to be involved in ovarian folliculogenesis. An anti-EXN32 monoclonal antibody (mAb) detects the protein in a high percentage of in breast, lung, ovary, and colo-rectal (CRC) cancers (high-to-medium intensity ranging from 30 to 70% in different cancer types. An analysis of high density tissue microarrays (300-700 highly characterized clinical specimens per each cancer) shows that EXN32 is over-expressed in all cancer stages and grades. In breast cancer, a EXN32 it is over-expressed in Her-2+, PR+ and ER+ patients and also in triple negative cases. In colon cancer, EXN32 is over-expressed both in B-RAF and K-RAS mutant and wild type cancers. We also found that EXN32 over-expression is statistically associated to a low activation of cadherin and beta-catenin pathways. Moreover, its expression is also associated with other prognostic and predictive markers. This evidence opens the way to further investigations on the EXN32 role in the marker-associated pathways. A characterization of the protein biological role showed that alteration of EXN32 expression strongly hampers cell proliferation, migration and invasiveness. The molecular pathways in which the protein is involved show that it plays a role in the Unfolded Protein Response and defence against oxidative stress. Our findings reveal that EXN32 is strongly affected by reticular stress induced by thapsigargin. In addition, EXN32 silencing during reticular stress protect cells from expressing the stress marker Bip/Grp78. In addition, EXN32 is involved also in handling of oxidative stress. Indeed, EXN32 silencing in cells exposed to 1% O2 hypoxia, causing a mitochondrial delivery of oxidants and hence sustaining oxidative stress, leads to inhibition of the Nrf2-mediated anti-oxidant response and to reduction of accumulation of HIF-1, the master transcription factor instructing cells to respond to hypoxic stress. We are investigating the possibility that EXN32 may participate as a molecular starter to the survival response induced by extracellular stresses. Results indicate EXN32 as a potential target for the design of novel drugs, such as aptamers, small molecules and protease inhibitors. For instance, molecules such as 2-PMPA and analogues are expected to inhibit EXN32 activity. Moreover, EXN32 and its specific mAb represent interesting tools for the molecular characterization of specific cancer subtypes. Investigations are ongoing to understand the prognostic and predictive value of EXN32. Citation Format: Matteo Parri, Alberto Grandi, Susanna Campagnoli, Elisa De Camilli, Alice Santi, Boquan Jin, Paolo Sarmientos, Guido Grandi, Giuseppe Viale, Paola Chiarugi, Luigi Terracciano, Piero Pileri, Renata Maria Grifantini. A novel potential therapeutic target for breast, lung, ovary and colon cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4384A. doi:10.1158/1538-7445.AM2015-4384A