A splenic mast cell tumor in an 11-year old Siamese cat: Medical oncology perspective
Dr. Emily Manor provides the medical oncology perspective on this challenging oncology case.
Dr. Emily ManorStaging is indicated in cats with splenic mast cell disease and includes obtaining radiographs to check for evidence of pulmonary metastasis (reported in 20% of cats in a necropsy study)1 and performing an abdominal ultrasonographic examination as well as a minimum database (CBC, serum chemistry profile, and urinalysis) and a buffy coat evaluation. In dogs with mast cell disease, it has been demonstrated that hepatic metastasis can exist without obvious change to the liver on ultrasound,2 so sampling of the liver (either by fine-needle aspiration and cytology or surgical biopsy at the time of splenectomy) is also indicated. The presence of disease outside of the spleen is an inconsistently reported prognostic indicator,3-5 and it has been shown in several studies that cats with splenic mast cell disease can have regression of metastasis after splenectomy.6,7 Therefore, the purpose of staging is mainly to establish a baseline prior to treatment since results are unlikely to change initial treatment recommendations and may not significantly affect prognosis. Full staging is also indicated in cats with primary gastrointestinal mast cell tumors or for cats with multiple cutaneous mast cell tumors, as there are reports of cats with primary splenic mast cell disease also having multifocal cutaneous lesions.3,8
Splenectomy is the treatment of choice for cats with splenic mast cell tumors, and adjuvant chemotherapy has not been shown to extend survival. A consensus on the efficacy of chemotherapy in feline mast cell disease is lacking, but limited information is available for both lomustine and toceranib. One study demonstrated a 50% overall response rate to lomustine in cats with mast cell tumors of varying locations.10 Recently, another study showed that up to 65% of feline splenic mast cell tumors have c-kit mutations,4 and responses to the oral tyrosine kinase inhibitor toceranib in cats with mast cell tumors of varying locations have been reported.11 A durable partial response to vinorelbine has been reported in a cat with metastatic intestinal mast cell tumor.12 And, anecdotally, responses have also been seen with vinblastine and chlorambucil. Chemotherapy should be considered for patients with metastatic disease that does not regress following surgery, in cases that have recurrence of disease after splenectomy, or in patients unable to undergo splenectomy because of owner preference or comorbidities.
H1 and H2 blockers are recommended in cats with gross mast cell disease to decrease the chance of histamine release and gastrointestinal ulceration. The efficacy of these drugs specifically for cats with mast cell tumors has not been evaluated. Prednisone is routinely used to treat canine mast cell disease, but it has not been evaluated in cats for this purpose, and, anecdotally, mast cell tumors in cats seem more resistant to corticosteroids compared with mast cell tumors in dogs.
A poorer prognosis for cats with splenic mast cell tumors has been reported in association with anorexia, male gender, significant weight loss,9 metastatic disease,4 lack of response to chemotherapy, and need for a blood transfusion.5 Median survival times are most commonly reported in the range of 12 to 19 months3,5,7,13; however, one study evaluating the outcome of cats undergoing splenectomy for various reasons reported a median survival of only 145 days for patients with splenic mast cell tumors.14 Often, even cats with metastatic disease or bone marrow involvement do very well following splenectomy and experience relatively long survival times.
Following treatment, intermittent restaging is recommended to monitor for disease recurrence or progression. This typically involves thoracic and abdominal imaging (with aspirates of liver and any enlarged lymph nodes) and a buffy coat evaluation. A rise in the number of mast cells in peripheral blood is concerning for disease recurrence and can be used as a marker of remission.
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3. Evans B, O'Brien D, Gregor T, et al. Treatment outcomes and prognostic factors of feline splenic mast cell tumors: a multi-institutional retrospective study of 64 cases, in Proceedings. Vet Cancer Soc Annual Conference 2015:43. (Abstract cited with permission from author.)
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