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Canine malignant mammary tumors: Prognostic and histopathologic studies
malignant mammary tumor
The study conducted for canine malignant mammary tumors consists of four parts including first, prognostic factors associated with survival two years after surgery in dogs with malignant mammary tumors; second, role of ovariohysterectomy (OHE) on dogs after surgical removal of mammary complex carcinomas; third, complete lifetime observation in dogs with various stages and types of mammary tumors; forth, identification of a mammary carcinoma with sebaceous differentiation. First, medical records of 79 female dogs with malignant mammary tumors were reviewed to identify prognostic factors associated with survival 2 years after surgery. Results of univariate analyses indicated that clinical stage, tumor size, ovariohysterectomy status, metastasis to adjacent lymph nodes or distant sites, and histologic classification of the tumor were significantly associated with survival 2 years after surgery. Tumors >= 5 cm in diameter and tumors that had been identified > 6 months before surgery were more likely to metastasize to adjacent lymph nodes. Ovariohysterectomy was more beneficial in dogs with complex carcinomas than in dogs with simple carcinomas. In multivariate analyses, clinical stage, tumor size, and ovariohysterectomy status were significantly associated with outcome 2 years after surgery. Second, to determine the effect of OHE on survival 2 years of female dogs with mammary complex carcinomas after surgical removal, 50 female dogs with mammary complex carcinomas were eligible for this study. Twenty-one dogs out of 50 dogs were with history of OHE performed prior to, after, or simultaneously with mammary tumor removal. OHE was conducted in 60% of dogs with stage I, II, or III tumors, and in 30% of dogs with stage IV or V tumors, respectively. Results showed dogs with mammary complex carcinomas undergoing OHE simultaneous with mammary tumor surgery have a reduced risk of death in 2 years. Although not statistically significant, a reduced risk of death in 2 years was found if OHE was done prior to mammary tumor surgery. Third, the study was conducted for complete lifetime observation in female dogs with various stages and types of mammary tumors. During the study period from 1998 to 2005, a total of 74 dogs diagnosed with mammary tumor after surgical treatment were followed up until death. It was found that approximately 50% of the dogs with mammary tumors died because of metastasis or local recurrence. They had an average survival time of 16.62 months after surgical removal, and an average life-span of 12.07 years. The results showed that although different stages or different types of the tumors were associated with the length of survival time after surgical removal, the length of total life span was similar among dogs with different tumor stages/types. Moreover, ovariohysterectomy (OHE) not only offered longer survival time after surgery, but also increased total life span in dogs with mammary tumors. Forth, this study identifies on an invasive mammary carcinoma with a rare distinctive feature characterized by sebaceous differentiation of tumor cells. This tumor occurred in a 10-year-old female mixed breed dog. The patient had two masses in the left 5th mammary gland. Grossly the masses were firm, whitish to light brown and superficially ulcerated. On cut surface, they were multilobulated with foci of necrosis. Microscopically, the tumors were composed of two distinctive neoplastic components, intraductal papillary adenocarcinoma and sebaceous carcinoma. The regions of sebaceous tumor were clumped separately, contained well-developed sebaceous cells and keratinized epithelial cells, and were surrounded by few to several layers of basaloid cells. The cells with abundant foamy cytoplasm that resembled sebaceous cells were also found within the intraductal papillary-like nests of mammary carcinoma providing evidence of sebaceous metaplasia. Sebaceous differentiation in a mammary gland tumor is possible because skin appendages and ductal apparatus of the mammary gland share a common anlagen. This tumor had an aggressive behavior with lymphatic metastasis. Consequentially, the dog had a poor prognosis.
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