Management of stage III benign mammary gland tumor in a 10-year-old female dog

A 10-year-old female German shepherd dog was presented with a large pendulous mass which was located in the area of the right inguinal mammary gland extending from M5–M2 with no marked lymphadenomegaly. The mass has progressively increased in size without regression over a period of 1 year. Radiography revealed a radiodense mass of tissue with no apparent metastasis to regional lymph nodes, no pulmonary metastases, and no abdominal viscera metastases. The tumor was staged as T3N1M0 after diagnostic clinical and radiological examinations based on WHO standards for tumor stage. Unilateral radical mastectomy with total mammary gland extirpation was performed and all glands from M5 to M1 on the right side were removed. The extirpated mass was 24 × 8 cm in size, weighed 2.25 kg, and was very firm. The tumor was lobular and was surrounded with thick band of fibrous capsule. Histology revealed numerous chondroblasts in the lacunae with moderate basophilic cytoplasm. These cells were monomorphic and pleomorphic (> 75% pleomorphic). There was anisocytosis and anisokaryosis. A good short-term clinical outcome was observed after surgical treatment and chemotherapy with tamoxifen and prednisolone for 21 days. Following clinical examinations, no pulmonary metastasis or recurrence of tumoral tissues was observed during 1-year post-surgery. Also, because the pathology of mammary gland tumors in dogs is similar to that of humans, it is strongly advocated that dogs are considered as natural animal model of human breast cancer research especially for testing new drugs and development of prophylactic and therapeutic measures.