+ general considerations

• Rhabdomyosarcoma is a very rare tumor which arises from pluripotential mesodermal cells of the urogenital ridge or similar cells in the Müllerian and Wolffian ducts during embryogenesis
• Rhabdomyosarcoma is characterized by local invasion with metastasis either rare or late in the course of disease
• Subtypes of rhabdomyosarcoma: embryonal, alveolar, and pleomorphic
• Subtypes are difficult to differentiate histologically and electron microscopy, immunohistochemistry (i.e., myoglobin and desmin) ± DNA ploidy may be required for definitive diagnosis
• Gross appearance: friable grape-like cluster or polypoid mass in the trigone or neck of the bladder causing urinary tract obstruction, hydronephrosis, and hydroureter
• Hypertrophic osteopathy without pulmonary metastasis is a common paraneoplastic syndrome
• Metastatic sites include mesentery, omentum, regional lymph nodes, adrenal gland, and liver

+ Signalment

• Young, large breed dogs < 2 years
• No sex predilection in dogs
• Breed predisposition: Saint Bernard

+ Clinical Signs

• Dysuria, hematuria, pollakiuria, and stranguria
• Vaginal discharge
• Urinary obstruction
• Incontinence

+ Urinalysis and Urine Sediment Cytology

• Hematuria and proteinuria are consistent findings on urinalysis due to ulceration of the urothelial mucosa
• Bladder wash cytology may improve diagnosis capabilities by reducing contaminants

+ Blood Tests

• Hematology and serum biochemistry findings are usually normal or non-specific
• Mild to moderate normochromic, normocytic anemia can be caused by either hematuria or bone marrow suppression secondary to chronic disease
• Uremia may result from neoplastic obstruction of urinary outflow or age-related renal failure

+ Survey Radiographs

• Imagining techniques include survey abdominal and thoracic radiographs, contrast radiography, and CT
• Survey radiographs: sublumbar lymph node enlargement, renomegaly, and metastatic disease in the pulmonary parenchyma or skeleton, particularly lumbar vertebrae and pelvis
• Positive contrast cystography is useful for identification of mucosal abnormalities and space occupying lesions
• Excretory urogram is indicated to determine the location and extent of obstructive urinary tract disease when the urethra cannot be catheterized

+ Ultrasonography

Ultrasonography is recommended to determine the location and extent of bladder involvement, regional lymph node size and appearance, and involvement of adjacent anatomical structures such as the colon

+ Biopsy

• Biopsy is required for definitive diagnosis of urinary tract tumors
• Biopsy techniques include FNA, needle biopsy, catheter biopsy, cystoscopic, and open surgery
• Percutaneous biopsy procedures are not recommended due to the risk of tumor seeding
• Catheter biopsy techniques correlate with surgical biopsy results in 73% of urethral and bladder tumors
• Inflammation secondary to necrosis and ulceration is common and may result in false-negative findings

+ Clinical Staging

Intergroup Rhabdomyosarcoma Study Committee Clinical Classification (postoperative staging system)

+ Surgery

• Surgical techniques for management of bladder tumors include:
• Palliative procedures: tube cystostomy ± partial cystectomy
• Curative-intent procedures: partial cystectomy and total cystectomy with urinary diversion
• Cystostomy tube can be placed percutaneously or with either laparoscopic or open surgery
• Complications: stranguria, pollakiuria, hematuria, urine leakage around the stoma, and vesicoureteral reflux which predisposes to ascending UTI and tumor seeding of the upper urinary tract

+ Chemotherapy

• Rhabdomyosarcoma is treated with a combination of surgery, radiation therapy, and chemotherapy in humans
• Chemotherapy agents include vincristine, actinomycin-D, and cyclophosphamide
• Prolonged clinical remission has been reported in 1 dog treated with partial cystectomy, cyclophosphamide, and doxorubicin
• Partial response has been observed with vincristine, doxorubicin, and cyclophosphamide, but single agent doxorubicin was ineffective in another case

+ Prognosis

• Prognosis for dogs with rhabdomyosarcoma is poor due to infiltrative growth and urinary tract obstruction
• Multimodality treatment, especially chemotherapy, has improved the prognosis in children with rhabdomyosarcoma
• Prognostic factors in humans include histologic type and grade, DNA ploidy, and clinical staging
• Diploid embryonal rhabdomyosarcoma are more sensitive to chemotherapy and radiation therapy than aneuploid embryonal rhabdomyosarcoma