POSITIVE IMMUNOHISTOCHEMICAL STAINING OF P53 AND CYCLIN-D IN ADVANCEDMOUSE SKIN TUMORS, BUT NOT IN PRECANCEROUS LESIONS PRODUCED BY BENZO[A]PYRENE

Squamous cell carcinomas (SCCs) of the mouse skin, as well as several types of preinvasive carcinoma precursor lesions, were produced by com plete carcinogenesis protocols with benzo[a]pyrene (B[a]P). Groups of mice were studied histologically at several time points. Tumors and pr ecursor lesions were systematically counted on microscope slides. The main feature of tumor development using this ubiquitous human carcinog en was the sequential appearance of in situ flat lesions with progress ive degrees of dysplasia. These changes, preceding the development of SCCs, were observed 20 weeks after beginning the carcinogen treatments . At this time point, in situ lesions outnumbered SCC similar to 10:1 at the higher total carcinogen dose examined. Ten weeks later, this ra tio was similar to 1:1. With the lower total carcinogen dose protocol, progression was delayed since at 27 weeks preinvasive lesions outnumb ered SCCs similar to 8:1. In addition to the in situ lesions, papillom as and keratoacanthomas were noted with the high B[a]P dose protocol, but tended to disappear at the end of the experiment, also indicating their probable role as SCC precursors. A study of histochemical marker s showed that gamma-glutamyltranspeptidase (GGT) and keratin 13, altho ugh good markers of malignant changes in early papillomas produced by two-stage carcinogenesis protocols,were mainly negative in dysplastic lesions produced by complete carcinogenesis with B[a]P. Immunohistoche mical detection of p53 showed that 50% of SCCs were positively stained , whereas only 3% of in situ lesions were p53 immunoreactive. Similarl y, 62% of SCCs were immunohistochemically positive for cyclin D, but n o precursor lesions were positive. Molecular analysis of the tumors sh owed the absence of H-ras mutations. No amplification of the cyclin-D- 1 gene was detected in eight SCCs examined. Collectively, these findin gs indicate that preinvasive in situ lesions are frequent during early stages of carcinogenesis when B[a]P is used in a complete carcinogene sis protocol. Although the absence of p53 immunoreactivity in this mou se model differs from the observed changes in human premalignant squam ous lesions, the sequence of morphological changes and the final incid ence of p53 and cyclin D staining abnormalities are very similar to th e well-known alterations that take place during human squamous carcino genesis.