Spontaneous tumors arising from mammary tissue are considered the most common tumor in female dogs and are of great importance both in veterinary and comparative medicine. Interleukin-15 is a cytokine involved in many physiologic processes such as activation of immune cells, autoimmune diseases, and cancer pathogenesis; however, the role of interleukin-15 in canine mammary cancers has not been well understood. We designed this study to examine the expression of interleukin-15 -IL-15- in canine mammary carcinoma by means of immunohistochemistry and any possible association with histologic malignancy grades, Bcl-2 expression, tumor recurrence, and overall survival. Results revealed that 14 -46.66%- of tumor samples strongly express IL-15, 7 cases -23.33%- moderately, and 9 cases showed weak immunoreactivity -30%-. The expression of interleukin- 15 is increased in canine mammary tumors in comparison to healthy tissues -p < 0.05-. Additionally, interleukin-15 higher expression is significantly in relationship with high histologic grade -p < 0.05-, high Bcl-2 expression -p < 0.05-, and shorter overall survival -p < 0.05-, but not with tumor recurrence -p > 0.05-. Interleukin-15 could have a role mammary carcinogenesis in dogs but more studies are needed to understand its exact roles.

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