Positive immunohistochemical staining of p53 and cyclin D in advanced mouse 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 complete carcinogenesis protocols with benzo[a]pyrene (B[a]P). Groups of mice were studied histologically at several time points. Tumors and precursor lesions were systematically counted on microscope slides. The main feature of tumor development using this ubiquitous human carcinogen was the sequential appearance of in situ flat lesions with progressive 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 approximately 10:1 at the higher total carcinogen dose examined. Ten weeks later, this ratio was approximately 1:1. With the lower total carcinogen dose protocol, progression was delayed since at 27 weeks preinvasive lesions outnumbered SCCs approximately 8:1. In addition to the in situ lesions, papillomas 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 markers showed that gamma-glutamyltranspeptidase (GGT) and keratin 13, although 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. Immunohistochemical detection of p53 showed that 50% of SCCs were positively stained, whereas only 3% of in situ lesions were p53 immunoreactive. Similarly, 62% of SCCs were immunohistochemically positive for cyclin D, but no precursor lesions were positive. Molecular analysis of the tumors showed the absence of H-ras mutations. No amplification of the cyclin-D-1 gene was detected in eight SCCs examined. Collectively, these findings indicate that preinvasive in situ lesions are frequent during early stages of carcinogenesis when B[a]P is used in a complete carcinogenesis protocol. Although the absence of p53 immunoreactivity in this mouse model differs from the observed changes in human premalignant squamous lesions, the sequence of morphological changes and the final incidence of p53 and cyclin D staining abnormalities are very similar to the well-known alterations that take place during human squamous carcinogenesis.
Mitsunaga
S I
SI
Department of Pathology, Fox Chase Cancer Center, Philadelphia, PA 19111, USA.
Zhang
S Y
SY
Ruggeri
B A
BA
Gimenez-Conti
I
I
Robles
A I
AI
Conti
C J
CJ
Klein-Szanto
A J
AJ
D000818:Animals; D001564:Benzo(a)pyrene / Q000633:toxicity*; D014408:Biomarkers, Tumor / Q000032:analysis*; D002294:Carcinoma, Squamous Cell / Q000139:chemically induced* / Q000737:chemistry* / Q000473:pathology; D016213:Cyclins / Q000032:analysis*; D004273:DNA, Neoplasm / Q000032:analysis; D018450:Disease Progression; D005260:Female; D011905:Genes, ras; D007150:Immunohistochemistry; D051379:Mice; D018632:Mice, Inbred SENCAR; D011230:Precancerous Conditions / Q000139:chemically induced* / Q000737:chemistry* / Q000473:pathology; D012878:Skin Neoplasms / Q000139:chemically induced* / Q000737:chemistry* / Q000473:pathology; D013194:Staining and Labeling / Q000379:methods; D016159:Tumor Suppressor Protein p53 / Q000032:analysis*
D014408:Biomarkers, Tumor; D016213:Cyclins; D004273:DNA, Neoplasm; D016159:Tumor Suppressor Protein p53; D001564:Benzo(a)pyrene