We have found a stem cell that is important for lung repair after injury that is located in a protected niche in the airway. After repeated injury, for example in smokers, these stem cells persist in an abnormal location on the surface of the airway and replicate and form precancerous areas in the lung. The presence of these stem cells in lung cancer tumors was associated with a poor prognosis with an increased chance of relapse and metastasis.This was especially true in current and former smokers. We therefore believe we have found a putative stem cell that is a tumor initiating cell for lung cancer. We developed a method to isolate these lung stem cells and to profile these cells and developed in vitro and in vivo models to assess their stem cell properties. Finally, we examined human blood samples to assess levels of surrogate markers of these stem cells to assess whether we could use this as a biomarker to predict the presence or absence of lung cancer in patients with a lung nodule.