ARTICLE ABSTRACTPurpose: Approximately one third of the patients with advanced non–small cell lung carcinoma (NSCLC) will initially respond to platinum-based chemotherapy, but virtually all tumors will progress (acquired resistance). The remainder will progress during initial treatment (primary resistance). In this study, we test whether the treatment can be improved by inhibiting hepatoma-derived growth factor (HDGF).Experimental Design: Thirteen primary NSCLC heterotransplant models were used to test four treatment regimens, including platinum-based chemotherapy with and without bevacizumab (VEGF-neutralizing antibody) or HDGF-H3 (HDGF-neutralizing antibody) and chemotherapy with bevacizumab and HDGF-H3. Expression of stem cell–related genes was measured using quantitative reverse transcription PCR (qRT-PCR) and immunohistochemistry.Results: Among 13 primary NSCLC heterotransplant models, three (23%) responded to chemotherapy but all relapsed within 20 days. The residual tumors after response to the chemotherapy exhibited an increased expression in 51 (61%) of 84 genes related with stem cell proliferation and maintenance, particularly those in Notch and Wnt pathways, suggesting enrichment for stem cell populations in the residual tumors. Interestingly, tumors from two of three models treated with HDGF-H3, bevacizumab, and chemotherapy combination did not relapse during 6 months of posttreatment observation. Importantly, this treatment combination substantially downregulated expression levels in 57 (68%) of 84 stem cell–related genes, including 34 (67%) of 51 genes upregulated after the chemotherapy.Conclusion: These data support the hypothesis that cancer stem cells (CSC) are a mechanism for chemotherapy resistance and suggest HDGF may be a target for repressing CSCs to prevent relapse of NSCLC sensitive to chemotherapy. Clin Cancer Res; 19(13); 3567–76. ©2013 AACR.