Clinical Rounds: A splenic mast cell tumor in an 11-year-old Siamese cat

The Clinical Rounds team is from the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, Knoxville, Tennessee.

Clinical rounds coordinator: Jeanne Larson, DVM, DACVIM (oncology)

Medical oncology: Emily Manor, DVM

Clinical pathology: Lisa Viesselmann, DVM

Radiology: Janina Bartels, DVM

Surgery: Jose Guevara, DVM

Anatomic pathology: Jade Fisher, DVM

Dr. Jeanne LarsonMast cell tumors are one of the most common causes of splenomegaly in cats, and they represent 15% to 26% of all feline splenic tumors.1,2 Other common primary locations for feline mast cell tumors include cutaneous tumors, which are often benign and cured with surgery, and intestinal tumors, which have a poor prognosis because of local invasion and frequent metastasis.3

Splenic mast cell tumors typically affect older cats.4 Most cats with splenic mast cell tumors do not have a history of cutaneous mast cell tumors, but there are some reports of splenic involvement in cats with multifocal cutaneous mast cell tumors.5 Clinical signs of splenic mast cell tumors may include vomiting, poor appetite and lethargy.4 Because of histamine release, gastrointestinal ulceration and anemia may also occur. Local and distant metastasis are common in cats with splenic mast cell tumors; the most common sites include the liver, visceral lymph nodes, peripheral blood, bone marrow, skin, lung and intestine.4

Case presentation

An 11 year-old castrated male Siamese cat was presented to the University of Tennessee (UT) internal medicine service for further evaluation of hepatosplenomegaly. He was initially presented to his referring veterinarian for losing his voice and polyuria/polydipsia. During the diagnostic workup, inflammation and mucus within the throat were noted on oral examination. Doxycycline was prescribed and the loss of voice resolved. Other diagnostic tests performed by the referring veterinarian included survey radiographs of the abdomen, and at this time incidental hepatosplenomegaly was identified. Referral for further evaluation was recommended.

Physical examination by the UT internal medicine service revealed a distended abdomen and a grade II/VI parasternal systolic heart murmur. A complete blood count (CBC), serum chemistry profile and urinalysis were performed. No significant abnormalities were noted on the CBC. The serum chemistry profile identified a mild elevation in blood urea nitrogen (BUN) concentration (51 mg/dl; reference range = 18 to 40 mg/dl). Urinalysis showed a urine specific gravity of 1.014 with 2+ proteinuria. Thoracic radiographs and abdominal radiography and ultrasonography were performed; findings included mild cardiomegaly, rounded liver margins with normal echogenicity and echotexture, marked splenomegaly with normal echogenicity, one mildly enlarged splenic lymph node (0.53 x 1.02 cm), other mildly enlarged mesenteric lymph nodes (about 0.6 cm), and a marked decrease in corticomedullary definition in both kidneys with moderate pyelectasia of the left kidney.

Fine-needle aspirates were obtained from both the spleen and liver with ultrasonographic guidance. Cytologic examination of the aspirates revealed numerous mast cells within the spleen, consistent with splenic mast cell neoplasia, and mild hepatic lipidosis with rare atypical mast cells within the liver. Omeprazole and diphenhydramine were prescribed, and the patient was transferred to the UT oncology service.

Tumor staging and treatment

Additional diagnostic tests performed through the UT oncology service included a buffy coat test, which was negative for circulating mast cells, and a preanesthetic echocardiographic examination, which revealed mild mitral regurgitation and no contraindication to anesthesia. After completion of cancer staging, splenectomy and biopsy of potential metastatic sites (including liver and abdominal lymph nodes) were recommended. Surgery was performed several days later by the UT soft tissue surgery service. At the time of surgery, a splenectomy and liver biopsy were performed. No enlarged lymph nodes were identified.

Histopathology of the spleen confirmed mast cell neoplasia. Liver biopsy revealed mild lymphocytic and neutrophilic periportal hepatitis and evidence of lipidosis.

Follow-up

Given the histopathologic findings of a splenic mast cell tumor with no evidence of regional or distant metastasis, adjuvant chemotherapy was not indicated and postoperative monitoring was recommended. The omeprazole and diphenhydramine were discontinued because no gross mast cell disease remained. Two months later, the patient was presented for re-evaluation. He was clinically doing very well at home. The results of a recheck buffy coat test were negative. The patient had continued mild proteinuria on urinalysis.

Three months later, the patient was presented again for re-evaluation. His owner reported mild lethargy over the past month. The results of a buffy coat test were negative, and a recheck abdominal ultrasonographic examination and examination of a liver aspirate showed no evidence of mast cell tumor recurrence or metastasis. A recheck CBC, serum chemistry profile and urinalysis revealed an inflammatory leukogram, moderate anemia (hematocrit 21.4%), and moderate azotemia (BUN = 94 mg/dl; creatinine = 3.2 mg/dl, reference range = 0.9 to 2 mg/dl). The urine protein to creatinine ratio was elevated at 1.8. A urine culture was submitted because of concern for pyelonephritis; the culture results were negative. Management for renal failure was instituted, including enalapril, iron injections, a renal diet and antibiotic therapy because of continued concern for pyelonephritis despite the negative urine culture result.

One month later, the patient presented for a recheck of his renal failure. Continued moderate anemia (hematocrit = 19.3%) and progressive azotemia were identified (BUN = 115 mg/dl; creatinine 3.4 mg/dl). Additional treatment recommendations included famotidine, darbopoeitin and subcutaneous fluids. Re-evaluation was recommended in two to four weeks. After that time, the patient was lost to follow-up.

References

1. Spangler WL, Culbertson MR. Prevalence and type of splenic diseases in cats: 455 cases (1985-1991). J Am Vet Med Assoc 1992;201:773-776.

2. Hanson JA, Papageorges M, Girard E, et al. Ultrasonographic appearance of splenic disease in 101 cats. Vet Radiol Ultrasound 2001;42:441-445.

3. Withrow SJ, Page R, Vail DM. Mast cell tumors. In: Small animal clinical oncology. 5th ed. St. Louis, Missouri: Elsevier, 2013.

4. Kraus KA, Clifford CA, Davis GJ, et al. Outcome and prognostic indicators in cats undergoing splenectomy for splenic mast cell tumors. J Am Anim Hosp Assoc 2015;51:231-238.

5. Litster AL, Sorenmo KU. Characterization of the signalment, clinical and survival characteristics of 41 cats with mast cell neoplasia. J Feline Med Surg 2006;8:177-183.

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