Abstract: A 9-year-old Rottweiler dog presented with right hind limb pain, lameness and mammary hyperplasia. The diagnosis was made by clinical observation, clinical examination, laboratory examination, imaging examination, surgical resection and exploratory laparotomy and histopathology. The results showed that the dog was mentally poor and its abdomen was obviously enlarged. Both the left and right sides of the penultimate second mammary glands were enlarged, visible breast area had a clear boundary, and the nipple was red and swollen with secretion of yellow fluid. The dog was slow in movement, reluctant to move, and had pronounced limp in right hind limb. The body temperature was 38.7 ℃. The total number of white blood cells, the number of neutrophils and the acute reaction protein（CRP）all increased. Decreased total red blood cell count, hemoglobin and hematocrit indicated infection and anemia. There were no obvious abnormalities in blood biochemical indexes. X-ray examination showed low bone density at the proximal tibia of the right hindlimb, loss of normal trabecular structure, destruction of bone cortex, and osteolysis. There was a large, nearly round, high-density mass in the midabdomen. A spherical dense mass was developed in the left posterior lobe of the lung. It can be initially diagnosed as invasive lesions of multiple sites and lesions. After surgical resection of the hyperplasia of the breast, an open abdominal exploration revealed a large tumor of 29 cm×20 cm×10 cm wrapped in the omentum with uneven surface. The tumor was not connected to other internal organs. There was a 4 cm×5 cm×8 cm tumor at the splenic head of the spleen with a ruptured capsule. The splenic and abdominal tumors were completely removed. Histopathological examination showed that the adenoid epithelial cells showed acinar hyperplasia in the breast tumor tissue, and the hyperplasia of the adenoid epithelial cells showed multiple layers or multiple layers of dense and disordered arrangement, and many spindle cells were found to be hyperplasia, which was a benign tumor. There was a large area of abdominal tumor tissue necrosis and bleeding. Tumor cells were oval, varying in size, nuclear round or oval, mostly located at one end with obvious nucleolus. There were more pathologic mitotic images, few interstitium, and multinucleated giant cells, similar to plasma cells, with some tumor cells undergoing necrosis. The histological morphology of splenic tumor was the same as that of abdominal tumor, and there were more mitotic images and megakaryocytes, which were malignant plasma cell tumors. A comprehensive analysis of clinical symptoms, laboratory examination, imaging examination and histopathological results confirmed that the dog had multiple myeloma.

Key words: multiple myeloma, dogs, histopathology