Reduced expression of p27/Kip1 is associated with the development of pulmonary adenocarcinoma

p27/Kip1 (p27), a negative regulator of cell proliferation, is a powerful prognostic marker in non-small cell lung carcinoma. To clarify the significance of p27 aberrations in the tumourigenesis of lung adenocarcinoma, p27 expression was investigated by immunohistochemistry in lung adenocarcinoma and its precursor lesion, atypical adenomatous hyperplasia (AAH), and correlated with the expression of Ki-67, cyclin Dl, and cyclin E. The p27 labelling index decreased in parallel with tumour progression (24.0% to 4.5%) and was found to be lower in neoplastic lesions than in normal bronchiolar epithelial cells (48.8%). There was a negative correlation between p27 and Ki-67 expression (p = -0.384, p<0.001). Cyclin E-positive lesions (with labelling index ≥5%) were found only in overt adenocarcinomas. The Ki-67 labelling index of cyclin E-positive, high (≥10%) p27 expressers was lower than that of cyclin E-positive, low (<10%) p27 expressers (16.8% vs. 42.6%; p = 0.046) and was similar to that of cyclin E-negative adenocarcinomas (15.0%). These results indicate that reduced p27 expression is associated with and may play a role in progression during the development of pulmonary adenocarcinoma.