The Clinical and Pathological Characteristics of Mammary Neoplasms with Malignant Mesenchymal Components in Female Dogs

Mammary neoplasms with malignant mesenchymal components are not common in female dogs, and they are poorly understood. As such, this study aimed to describe the clinical presentation, histological findings, and the COX-2 immunohistochemical expression of mammary neoplasms in female dogs with malignant mesenchymal components, as well as verify the relationships between the different neoplasm types and these aspects. We selected 41 female mammary neoplasms (23 carcinosarcomas, 16 sarcomas, and 2 sarcomas in mixed tumors). Medical records were reviewed to obtain clinical data. Subsequently, histological slides were analysed to establish histological parameters, and immunohistochemistry was used to assess the expression of COX-2 receptors. Carcinosarcomas and sarcomas developed as large tumours, mainly in the abdominal and inguinal mammary glands, with frequent intratumoral necrosis and a low frequency of nodal metastasis. Fifty-eight percent of the cases of malignant mesenchymal proliferation were identified as osteosarcomatous, and 24.5% chondrosarcomatous and fibrosarcomastous each. The osteosarcomatous pattern was the most predominant type in sarcomas and carcinosarcomas, and was the only one that resulted in vascular invasion, regional lymph node metastases, and higher histologic grades. High COX-2 expression was detected in 10% of the carcinosarcomas and 25% of the sarcomas. In conclusion, sarcomas and carcinosarcomas showed similar results regarding the clinical and pathological aspects. Discovering carcinosarcomas and sarcomas with high COX-2 expression suggests that, in some cases, these neoplasms may respond to therapy with COX-2 inhibitors.