Sarcoma of the prostate is a rare neoplasm that accounts for 0.1–0.2% of all primary prostatic malignancies in humans.5,9 Most prostate sarcomas (67%) are of muscle origin, with rhabdomyosarcoma occurring in children and leiomyosarcoma predominating in adults.11 In the dog, prostatic leiomyosarcoma is also rare; only 4 cases have been documented.4,6 In 1 report, a single leiomyoma but no leiomyosarcomas were noted among 23 canine prostatic tumors.8 The WHO Bulletin makes no specific reference to prostatic leiomyosarcoma in animals other than to state that poorly differentiated spindle cell tumors of the prostate could not be further classified.2 In this report, we document a primary prostatic leiomyosarcoma with metastasis in an adult dog. The histomorphologic diagnosis was verified using immunohistochemical techniques. A 10-year-old intact male Boxer was referred to the Veterinary Teaching Hospital, College of Veterinary Medicine, University of Minnesota, with a history of stranguria and urinary incontinence of 2 days duration. Physical examination revealed a distended urinary bladder. Clinicopathologic studies revealed a mature neutrophilic leukocytosis (25.7 3 103 neutrophils/ml; reference range, 2.1–11.2 3 103 neutrophils/ml),a increased serum creatinine (3 mg/dl; reference range, 0.5–1.5 mg/dl),b increased serum urea nitrogen (49 mg/dl; reference range, 7.0–28 mg/dl),b and hyperglycemia (213 mg/dl; reference range, 77–116 mg/dl).b A catheter was passed into the urinary bladder, and an estimated 2.5 liters of urine was removed. Urinalysis revealed dilute urine (1.016 urine specific gravity) and pyuria (10–12 white blood cells [WBC]/high-power field [HPF]; reference range, ,5 WBC/HPF). Abdominal radiographs revealed a large mid abdominal mass and a smaller calcified mass in the caudal abdomen. The dog died 12 hours after being hospitalized. Necropsy revealed gastric dilatation/volvulus and a distended urinary bladder. The prostate was asymmetrical, firm, and 7.0 3 5.0 3 3.0 cm. The cut surface revealed a pale capsular region and a mottled beige to tan parenchyma with multiple cysts 0.5–1.0 cm in diameter (Fig. 1). A large periprostatic cyst, 11.0 3 9.0 3 7.0 cm, was situated at the base of the prostate dorsocaudal to the urinary bladder. The cyst wall was mineralized, and the lumen contained many hard spike-like concretions and thick brown fluid. The left ureter was markedly dilated, about five times that of the right ureter, and multiple firm nodules, 0.3–0.5 cm in diameter, were scattered along the serosal surface. The urinary bladder was

Diagnosis of malignant histiocytosis (MH), a disorder characterized by systemic proliferation of morphologically atypical histiocytes and their precursors, in an 8-year-old neutered female Golden Retriever was based on light and electron microscopic and immunohistochemical findings. Clinically, the dog presented with unilateral forelimb lameness. Eight days after surgical exploration of a swollen brachium, the dog developed sudden onset of posterior paresis, fecal and urinary incontinence, and a flaccid tail. Necropsy revealed infiltrative and nodular lesions in the right forelimb and regional lymph nodes, thoracic and abdominal cavities, and lumbar epidural space. Gross lesions were not found in the lungs or integument. Histopathologic examination showed infiltrates of atypical histiocytes in skeletal muscle, joint, and regional lymph nodes of the right forelimb; intercostal muscle; lung; liver; spleen; pancreas; kidneys; and spinal dura. Most tumor infiltrates were nodular and composed of loosely aggregated cells that were 10-30 microns in diameter with abundant eosinophilic to foamy cytoplasm, had central or eccentric nuclei, and were periodic acid-Schiff negative. Many binucleated cells, multinucleated giant cells, and mitotic figures were seen. Tumor cells contained phagocytosed erythrocytes, mononuclear cells, and some leukocytes. Ultrastructural features of tumor cells included cytoplasmic lipid droplets, lysosomes, and phagolysosomes. Immunohistochemical studies on paraffin-embedded sections showed positive reactivity to human T-cell Ag (clone UCHL-1) and for lysozyme, alpha-1-antitrypsin, and cathespin B. Polyclonal intracellular immunoglobulin reactivity and lectin binding (peanut, soybean, and wheat germ agglutinins and concanavalin A) were also demonstrated. Criteria for diagnosis of malignant histiocytic tumors and differential diagnosis are discussed.

Aspirin disposition in immature and adult dogs, assessed by plasma salicylate concentrations following single doses of aspirin given orally (p.o.) and intravenously (i.v.), was compared. Using a cross-over design, four immature (12-16-weeks-old) and eight adult (1-2-years-old) dogs were given a single dose of aspirin at 17.5 mg/kg body weight i.v. and a single dose of buffered aspirin at 35 mg/kg body weight p.o. Blood was collected from the jugular vein for 24 h following each dose. A fluorescence polarization immunoassay was used for determination of salicylate in plasma. Significant differences in aspirin disposition were identified between the two groups. Immature dogs had significantly shorter salicylate half-life, lower mean residence time, and more rapid salicylate clearance than adult dogs. The difference in volume of distribution between the two groups was not significantly different. Immature dogs had lower mean (+/- SD) peak plasma salicylate concentrations (64.5 +/- 2.38 mg/L) than adult dogs (95.9 +/- 12.2 mg/L) following a single oral dose of buffered aspirin at 35 mg/kg body weight. Predicted plasma salicylate concentration-time curves were constructed for various aspirin dosage regimens. This analysis showed that the previously recommended buffered aspirin dose for adult dogs of 25 mg/kg body weight p.o. every 8 h would be ineffective in maintaining plasma salicylate concentrations > 50 mg/L in immature dogs.

The effect of tamoxifen citrate on bone mass in immobilization osteoporosis was studied in 11 growing dogs. Immobilization osteoporosis was induced by fiberglass cast immobilization of the right hindlimb for 28 days, while the left hindlimb served as a nonimmobilized control. Six dogs received tamoxifen citrate (1.5 mg/kg per os) once daily for 28 days; five dogs received no treatment. All dogs were euthanatized on day 28 and bone samples were collected. Bone mineral content of the distal tibial metaphysis of casted and uncasted limbs was measured by single photon absorptiometry. Immobilization resulted in a significant reduction in bone mass in the casted limb of untreated and tamoxifen-treated dogs. However, tamoxifen-treated dogs had less severe immobilization osteoporosis than untreated dogs. The calculated bone mass sparing effect of tamoxifen was 24.4%. Because of the complexity of pathologic bone remodeling, use of a single therapeutic agent may not be the optimal means of preventing bone loss associated with immobilization.

The effect of acetylsalicylic acid (aspirin) on bone mass and bone prostaglandin E (PGE) in immobilization osteoporosis was studied in 12 growing dogs using a unilateral hind limb cast-fixation model. Osteoporosis was induced by fiberglass-cast immobilization of the right hind limb for 4 weeks, with the left hind limb as a control. Six dogs received buffered aspirin at 25 mg/kg body weight per os every 8 hours; 6 dogs received no treatment. All the dogs were killed after 4 weeks, and bone samples were collected. Bone mineral content of the distal tibial metaphysis was measured by single-photon absorptiometry. In vitro release of PGE from the calcaneus, tibial cortical bone, tibial cancellous bone, and ilium were measured using a specific radioimmunoassay for PGE. Compared with the controls, the casted limb of untreated dogs had half the bone mass and a twofold increase in bone PGE. Aspirin treatment was associated with a 65 percent reduction in bone PGE and a 13 percent bone mass sparing effect. These results provide indirect evidence that PGE plays a role in immobilization osteoporosis.

Intramedullary spinal cord metastasis (ISCM) was diagnosed in three dogs with signs of myelopathy. The clinicopathologic features of ISCM in these and previously reported cases in the veterinary and human literature were compared. Myelopathic signs associated with ISCM may be the initial clinical manifestation of malignancy or may develop in the patient with known malignancy. Pain, a frequent manifestation of extradural compressive myelopathy, is not a consistent feature of ISCM. Survey spinal radiographs are usually unrewarding and cerebrospinal fluid (CSF) abnormalities nonspecific. Myelography is indicated to differentiate intramedullary lesions from more common extradural compressive lesions. Myelographic interpretation may be difficult, and intramedullary tumors must be differentiated from spinal cord edema or hemorrhage. Evidence of widely disseminated malignancy should increase suspicion for ISCM; hemangiosarcoma and lymphosarcoma should be considered the most likely histologic types. CSF cytology may be helpful in the diagnosis of patients with lymphosarcoma. Prognosis is poor due to the frequent presence of disseminated disease, although temporary response to corticosteroid therapy may be achieved. More aggressive therapeutic approaches, such as spinal irradiation and microsurgical resection of metastases, have been advocated in humans but have not been reported in the dog. Although it is an uncommon complication of systemic malignancy, ISCM should be considered in the differential diagnosis of myelopathy in the dog.

A retrospective analysis of 85 dogs with hemangiosarcoma (HSA) that underwent complete necropsy, including gross examination of the brain, was conducted. Grossly identifiable intracranial lesions were present in 17 dogs. Twelve of 85 dogs (14.2%) had brain metastases. Four of 85 dogs (4.7%) had hemorrhagic lesions and/or ischemic necrosis without identifiable tumor. One dog had a primary central nervous system tumor. Signs of intracranial disease were present in six of 85 dogs (7.1%) with HSA; four had brain metastases and two had nonneoplastic lesions. Metastases had a propensity for cerebrum and gray matter. Dogs with brain metastases had more widely disseminated disease than dogs without brain metastases (P less than 0.001). Dogs with pulmonary metastases were at greater risk for developing brain metastases than dogs without pulmonary metastases (odds ratio = 8.31). Although thoracic radiography accurately identified ten of 12 dogs (83%) with pulmonary metastases, too few cases were available to assess the applicability/accuracy of thoracic radiography in predicting the presence or absence of brain metastases in dogs with malignancy and signs of intracranial disease.