Figure 5.

Lack of neuroendocrine (NE) differentiation in NNK-induced tumors, following 24 weeks NNK exposure plus 6 weeks recovery. Left panel: Tumor mass (T) is stained with hematoxylin and eosin (H&E). Middle and right panels: Immunohistochemical reactivity is found only in NEBs (arrows) for synaptophysin (SYP) and ASCL1, respectively, whereas tumor (T) shows no NE immunoreactivity. Sections were stained using ABC peroxidase and DAB, followed by counterstaining with light green SF (ASCL1 staining intensified with nickel sulfate). Lu: airway lumen. Scale bar: 50 µm.