Caracterização das cavidades císticas de carcinomas micropapilares mamários em cadelas e avaliação da transição de áreas in situ para áreas invasoras

Abstract

Invasive micropapillary carcinoma (IMC) of the mammary gland is a tumor that affects humans and dogs and is characterized by aggressive behavior. The cystic cavities, tumor microenvironment, and transition from in situ to invasive areas in this tumor type remain poorly understood. This study aimed to characterize cystic cavities and investigate the neoplastic cells and tumor microenvironment permeating these cavities in in situ, transition, and invasive areas of canine mammary gland IMC, drawing a comparison with IMC in humans. The methods employed included histopathological evaluation and histochemical analysis using PAS, Alcian Blue (pH 2.5), Alcian Blue-PAS, toluidine blue, and oil red. To assess the basement membrane and secretion, immunohistochemical and immunofluorescence analyses were performed to evaluate myoepithelial markers (p63, calponin-1, smooth muscle myosin, smooth muscle alpha-actin, cytokeratin 14, and vimentin), as well as other characterization parameters (pancytokeratin, factor VIII, caspase-3, epithelial membrane antigen, collagen IV, and N-cadherin). Additionally, transmission electron microscopy (TEM) was used for ultrastructural evaluation of the cells lining the cavities, neoplastic epithelial cells, and the tumor microenvironment. The diameter of collagen fibers was measured in IMC areas and normal mammary glands via TEM, and statistical analysis was performed using the Kruskal-Wallis test and Dunn’s post hoc test. With these analyses, it was possible to determine that the cystic cavities of IMC in female dogs were lined by modified myoepithelial cells that rest on a discontinuous, disorganized, or absent basement membrane. Neoplastic epithelial cells exhibit a basal immunophenotype and an epithelial-mesenchymal transition profile, along with mixed mucosubstances and intracellular neutral lipids. Apoptotic neoplastic epithelial cells were observed at the periphery of the micropapillary transitional areas, which may be related to the progression to invasive areas. PAS-positive neutral glycoproteins were secreted within the cavities. The stroma was rich in cancer-associated fibroblasts interspersed with collagen fibers of heterogeneous sizes, with larger diameters observed in invasive areas. This study represents an initial milestone in the detailed characterization of canine IMC cavities. It highlights their structural and functional complexity, suggesting that these cavities play a fundamental role in tumor progression mechanisms. The similarity between canine and human IMCs underscores the translational potential of the canine model for investigating tumor biology and progression mechanisms.