A new clinical trial will investigate the safety of vantictumab (OMP-18R5), a new lung cancer drug targeting cancer stem cells (CSCs). CSCs, the actively multiplying cells responsible for generating tumors, are thought to be central in cancer relapse by 'repopulating' tumors, even if the bulk of the tumors cells are destroyed during treatment. Vantictumab blocks the Wnt pathway, a key molecular signaling pathway used by CSCs. Patients with previously treated advanced non-small cell lung cancer (NSCLC) will receive vantictumab in combination with the chemotherapy agent docetaxel (Taxotere). In addition to the safety of the drug combination, the trial will also investigate how effective it is and whether any biomarkers predict how well patients respond.