General Considerations

•retroperitoneal sarcomas are defined as mesenchymal tumors originating from within the retroperitoneal space but not including neoplasms arising from retroperitoneal organs, such as the adrenal glands, kidneys, and ureters

•HSA is the most common retroperitoneal sarcoma in dogs (64%, 9/14), with others including OSA, peripheral nerve sheath tumor, and leiomyosarcoma

•majority of dogs with retroperitoneal sarcomas have a high histologic grade (grade III in 57%) and clinical stage

•50% (7/14) retroperitoneal sarcomas are invasive into structures such as the kidney, adrenal glands, aorta, caudal vena cava, and paraspinal muscles

•metastasis is present in 29% (4/14) dogs at diagnosis and 71% (10/14) dogs at death

•lungs are the most common site of metastasis, and other sites include peritoneum, intestines, liver, heart, and brain

Clinical Features

•large breed dogs with a median weight of 27.7 kg

•median age 9 years

•clinical signs are either non-specific or neurologic

•non-specific signs include inappetence, lethargy or collapse, and weight loss

•neurologic signs include LMN pelvic limb lameness and neurogenic urinary incontinence

•hematology: anemia is common (71.4%) with other abnormalities including leukocytosis, lymphopenia, neutrophilia, thrombocytopenia, and red blood cell morphologic abnormalities

•serum biochemistry: AST and creatine kinase were increased in ≥ 50% dogs

•diagnosis: retroperitoneal mass is readily evident on abdominal imaging using survey radiographs, ultrasound, or CT

Treatment

•exploratory celiotomy and surgical resection

•± radiation therapy in either a preoperative, intraoperative, or postoperative setting

•± adjuvant chemotherapy

Prognosis

•prognosis is poor with 37.5 day MST and tumor-related deaths in 93% (13/14) dogs (range, 2-498 days)

•local tumor recurrence in 14% (2/14) dogs and tumor progression in 43% (6/14) dogs

•metastasis is present in 29% (4/14) dogs at diagnosis and 71% (10/14) dogs at death

•prognosis for retroperitoneal sarcoma is also poor in humans with prognostic factors include tumor grade and ability to achieve complete microscopic and macroscopic surgical resection

•5-year survival rate of 69%-92% for grade I retroperitoneal sarcomas is significantly better than 16%-48% for grade II and III retroperitoneal sarcomas

•complete excision results in a significant survival benefit with a 41-103 month MST and 43%-72% 5-year survival rate compared to 9-18 months and 3%-33%, respectively, following incomplete resection