The relationship between p21/waf1 expression patterns and cell proliferation during the tumorigenesis of the bronchus.

Each developmental stage in the process towards bronchial squamous cell carcinoma (normal epithelium, squamous metaplasia and early stage squamous cell carcinoma including in situ carcinoma) was examined for p21/waf1 protein expression and cell proliferation using MIB1. P21/waf1 immunoreactivity was classified into four patterns: predominantly cytoplasmic staining, exclusively nuclear staining, both nuclear and cytoplasmic staining and negative. The cases with predominantly cytoplasmic staining showed suppression of cell proliferation. Most cases with either negative or exclusively nuclear staining revealed high cell proliferation. The simultaneous evaluation of p21/waf1 and cell proliferation is valuable for clinical determination of the high risk for malignant transformation.