ALVEOLAR STEM-CELLS IN CANINE BRONCHIAL CARCINOGENESIS

Alveolar type II cells are not present in normal epithelium of canine segmental bronchi but after carcinogen exposure they do occur in intra -epithelial lesions with all degrees of atypia and in invasive lesions with different glandular growth patterns. Immunohistochemistry for pr oliferation markers (PCNA; Ki-67) strongly suggest that such novel typ e II cells are pluripotential stem cells in canine bronchial carcinoge nesis. Very likely, bronchial carcinogenesis is subject to an oncofeta l mechanism of differentiation: bronchial epithelial retrodifferentiat ion followed by novel differentiation of alveolar tumor stem cells.