Tumores mamários mistos caninos: análise do DNA mitocondrial e da expressão protéica de HER2 e EGFR nos componentes epitelial e mesenquimal

Abstract

Benign mixed tumors are histologically characterized by a mixture of epithelial and mesenchymal components. These are common neoplasias in canine mammary glands and can malignize developing carcinomas in benign mixed tumors. The cell origin of the differentcomponents that compose mixed tumors and the aspects that determine its malignant transformation remains to be elucidated. The aims of this study were: 1) To investigate alterations in a polymorphic region of the mtDNA control region and the presence of polymorphisms in nuclear microssatellites loci in canine mammary mixed tumors to accessthe clonal pattern. 2) To study the expression of HER2 and EGFR oncoproteins in canine mammary mixed tumors and verify the possible role in histogenesis and progression of these tumors. The epithelial and mesenchymal components were microdissected from 10 benignmixed tumors and 9 carcinomas in mixed tumors. The DNA was extracted and a 273bp fragment from mitochondrial control region was amplified using polymerase chain reaction and then sequenced. The nuclear microssatellites loci: FH2658, ren214L11, FH2010, FH2263 e FH39 were also analysed. Additionally, immunohistochemical expression of HER2 and EGFR was analyzed in 16 benign mixed tumors and 22 carcinomas in mixed tumors. Nine polymorphism and four mutations were found. Identical haplotype of mitochondrial DNA in both the epithelial and mesenchymal components were found in 80.0% (8/10) of the benignmixed tumors and in 89% (8/9) of the carcinomas in benign mixed tumors. Amplification of microssatellites locus was obtained in only one case of benign mixed tumor and one case of carcinoma in mixed tumor and the same allelic pattern for the five loci was observed in bothepithelial and mesenchymal components. Overexpression of HER2 and EGFR was found in 9% (2/22) and 31.8% (7/22) of carcinomas in mixed tumors. In both the cases the overexpression was restricted to the epithelial component. HER2 and EGFR were not overexpressed in benign mixed tumors, however an inconclusive staining was found in 12.5% of cases. In conclusion, the epithelial and mesenchymal components of tumors showed the same haplotype of mitochondrial DNA suggesting a shared clonal origin. The results indicate that HER2 overexpression may not be associated with acquisition of malignant phenotype in carcinomas um mixed tumors. In contrast, EGFR may be a role in the divergence and malignization of these tumors, however are not involved with mesenchymal differentiation.