Most mammary tumors in pet rabbits are carcinomas; prognostic factors are unknown. The aim of this study on rabbit mammary carcinomas was to determine the expression of myoepithelial markers that have a prognostic relevance in human cancers. Mammary carcinomas (n = 119) of female or female-spayed pet rabbits were immunostained for cytokeratin AE1/AE3, vimentin, smooth muscle actin (SMA), and calponin; and percentages of non-neoplastic myoepithelial cells (ME cells) and calponin-positive neoplastic cells were determined. Using statistical analysis, data were correlated with the age of the rabbits and histological tumor characteristics. All carcinomas contained retained spindle-shaped ME, while 115 also contained hypertrophic ME (HME). A statistically significant relationship existed between a higher age and an increase in HME. In 111 carcinomas (93%), tumor cells expressed calponin. There was a significant correlation between higher percentages of calponin-positive tumor cells and a lower mitotic count, an increased percentage of tubular growth, and a lower grading score, respectively. Data suggest that pet rabbit mammary carcinomas develop from progression of in situ cancer and that the extent of calponin expression in tumor cells influences their biological behavior. These results provide the basis for a long-term follow-up on the prognostic significance of calponin expression in mammary cancer cells.
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