Validation of a low-cost modified technique for constructing tissue microarrays for canine mammary tumor analysis

Compared with conventional histological paraffin blocks, tissue microarray (TMA) represents a "high-throughput tool" that provides rapid results, a time- and cost-effective approach and simultaneous investigation of several tissue samples under the same conditions. Given the large number of cases of dogs affected with mammary tumors, the complexity of these tumors and their similarity with breast cancer in women, this study aimed to validate a low-cost modified method to construct TMAs for canine mammary tumor analysis using immunomarkers. Carcinoma cases were selected from canine mammary carcinomas in mixed tumors (CMT) because this tumor type is the most heterogeneous among the histopathological types of mammary tumors observed in female dogs. Through a histopathological examination, tumor representativity was compared between conventional sections and histological sections obtained from the TMA block; both were stained with hematoxylin and eosin. An immunohistochemistry analysis was performed to compare the percentages of immunoreactive cells obtained in whole tissue sections versus those obtained from sections from the TMA block. Streptavidin-biotin peroxidase complex and anti-PCNA, anti-vimentin and anti-pancytokeratin antibodies were used. Statistical analysis consisted of the nonparametric Friedman's test (p≤0.05) and descriptive statistical analysis. Histopathological analysis showed tumor representativity in all TMA cores selected for the study. There was no difference between the immunohistochemical analysis of mammary tumors using conventional histological sections or sections obtained from a single 1-mm-diameter TMA core, regardless of the marker used: PCNA (p=0.279), pancytokeratin (p=0.243) and vimentin (p=0.967). The results did not change even when the means of any number of cores were compared among each other and with the conventional histological section: PCNA (p=0.413), pancytokeratin (p=0.177) and vimentin (p=1.0). Therefore, this study validates the use of a low-cost and modified TMA construction technique proposed by Pires et al. for canine mammary tumor analysis.