Combined and sequential expression of p53, Rb, Ras and Bcl-2 in bronchial preneoplastic lesions

Several simple molecular abnormalities have been detected in bronchial preneoplastic lesions, but the simultaneous presence of these alterations has been scarcely investigated.

We studied, by an immunohistochemical method, the expression of p53, Rb, Ras and Bcl-2 in 65 samples from surgical specimens and diagnostic biopsies selected for the presence of preneoplastic changes in the bronchial epithelium. To perform an analysis of the combined expression of all markers in the same areas, we accurately mapped every consecutive section on which immunohistochemical reactions were performed, subdividing each specimen into 25x microscopic fields, which allowed good topographical mapping.

It was found that the frequency of p53-positive and Rb-negative microscopic fields was directly related to the morphological grading of lesions. On the other hand, Ras expression characterized high-grade lesions not showing squamous differentiation (non-squamous Cis). Regarding Bcl-2 expression, only slight differences in positivity distribution were found between the different lesions. More interesting was the parallel evaluation of all markers in the same areas: one of the main patterns, found to be correlated with the severity of histopathological features, was characterized by combined p53 hyperexpression/Rb hypoexpression; furthermore, when Ras and Bcl-2 hyperexpression were superimposed to the above pattern, the former mainly characterized non-squamous Cis, while the latter was present only in high-grade squamous lesions. However, the most frequently encountered pattern did not show any alteration of the studied markers, suggesting that other mechanisms could be involved in bronchial carcinogenesis.

The detection of combined molecular abnormalities in bronchial preneoplasia could clarify the steps involved in lung carcinogenesis; furthermore, a simple and inexpensive method, such as immunohistochemistry, could be routinely applied also to cytologic specimens in order to detect those lesions, or patients, that are prone to progression towards lung cancer.