Background: Lung cancer is the leading cause of cancerrelated mortality worldwide with a 5 year survival rate of 15%. Non-small cell lung cancer (NSCLC) is the most commonly diagnosed form of lung cancer. Cisplatin-based regimens are currently the most effective chemotherapy for NSCLC, however, chemoresistance poses a major therapeutic problem. New and reliable strategies are required to avoid drug resistance in NSCLC. Cell division cycle associated 3 (CDCA3) is a key regulator of the cell cycle. CDCA3 modulates this process by enabling cell entry into mitosis through degradation of the mitosis-inhibitory factor WEE1. CDCA3 itself is also degraded in G1 yet reexpressed in G2/M phase, to allow successful progression through the cell cycle. Herein, we describe CDCA3 as a novel prognostic factor in NSCLC and target to delay or prevent cisplatin resistance in NSCLC. Methods: CDCA3 expression was investigated in squamous and non-squamous NSCLC using several approaches including bioinformatic analysis of publicly available datasets, immunohistochemistry of a tissue microarray and western blot analysis of matched tumor and normal tissue and NSCLC cell lines. CDCA3 function in NSCLC was determined using several in vitro assays by siRNA depleting CDCA3 in a panel of three immortalized bronchial epithelial cell lines (HBEC) and seven NSCLC cell lines. Results: CDCA3 transcripts and protein levels are elevated in NSCLC patient tissue and highly expressed in tumor cells relative to proximal normal cells. High mRNA levels are associated with poor survival in resected NSCLC. Depletion of CDCA3 in vitro markedly impairs proliferation in seven NSCLC cell lines by inducing a mitotic cell cycle arrest, ultimately resulting in p21- dependent cellular senescence. Importantly, silencing of CDCA3 also greatly sensitizes NSCLC cell lines to cisplatin. In line with these in vitro data, NSCLC patients that have elevated levels of CDCA3 and are treated with cisplatin have a poorer outcome than patients with reduced levels of the protein. To improve patient response to cisplatin, we are exploring novel strategies to suppress CDCA3 expression in tumor cells. Conclusion: Our data highlight CDCA3 as a novel factor in mediating NSCLC. We propose that evaluating novel strategies to target CDCA3 may prove a useful strategy is enhancing the anti-tumor activity of platinum-based chemotherapy and may ultimately benefit patient outcomes by preventing cisplatin resistance.