NNK induced a time-dependent IGF-1R phosphorylation in primary cultured normal human lung epithelial cells derived from large airways (NHBE), the precursor cells for squamous cell carcinomas, or small airway epithelial cells, the precursor cells for adenocarcinomas (Fig. 2a), and in various immortalized, normal human bronchial epithelial cell (HBE) cell lines, including HB56B and BEAS-2B (Fig. 2b). Here, IGF1R is linked to squamous cell carcinoma.