Page 1263 - Cote clinical veterinary advisor dogs and cats 4th

Mast Cell Tumors, Cat 633

splenic/hepatic enlargement/infiltration,
GI mass or diffuse thickening), bone
VetBooks.ir in most cases with a normal CBC), Diseases and Disorders
marrow aspiration (p. 1068); low yield
splenic/liver aspiration (p. 1112), and
fluid analysis (p. 1343).
Visceral forms (spleen, GI tract):
• Cats with visceral MCTs should have
complete staging before definitive therapy.

Advanced or Confirmatory Testing
• The histologic grading system used for
canine cutaneous MCTs is not applicable for
cats.
• Histologic subtypes for feline cutaneous
MCTs include mastocytic well-differentiated,
mastocytic pleomorphic, and atypical/
poorly granulated tumors. The mastocytic
pleomorphic type has a higher mitotic index
MAST CELL TUMORS, CAT This right lip MCT was present for several months before presentation and had
not changed in size. The pink, hairless mass with mild, superficial ulceration is typical. and a worse prognosis.
• Subtypes cannot be defined cytologically. KIT
mutations occur in the majority of cutaneous
or splenic MCTs but have not been shown
to be prognostic for survival.
lymph nodes may be normal in size even Differential Diagnosis
with metastasis. About 15% of cats with • Cutaneous form: basal cell tumor, hair follicle TREATMENT
cutaneous MCTs have concurrent splenic or sweat gland tumor, squamous cell carci-
or visceral MCT. noma, hemangioma/sarcoma, lymphoma, Treatment Overview
• Visceral MCTs: splenomegaly, ascites, eosinophilic granuloma complex, and lipoma In most cases, the goal of therapy is to control
abdominal mass, bowel wall thickening, • Splenic form: hemangiosarcoma, lymphoma, the local disease with surgery or possibly radia-
abdominal pain, and mucous membrane infectious splenitis, myeloproliferative disease tion therapy (RT) to prevent recurrence and
pallor secondary to anemia are possible. • GI masses or diffuse infiltration of the GI metastasis. In cases presenting with metastasis
tract: lymphoma, intestinal adenocarcinoma, or nonresectable local disease, the goals are to
Etiology and Pathophysiology inflammatory bowel disease, leiomyosarcoma, minimize tumor volume and secondary GI signs
• Mast cells participate in allergic and inflam- histoplasmosis, or granulomas and to maintain quality of life.
matory responses and are normally found
in skin, visceral organs, bone marrow, and Initial Database Acute and Chronic Treatment
lungs. Cutaneous form: Cutaneous form:
• Mast cells harbor preformed granules that • FNA of the lesion for cytologic exam: cyto- • Surgery is the primary treatment for cutane-
contain histamine, heparin, and other logically, mast cells have a round nucleus and ous MCTs.
cytokines that are released on activation of intracytoplasmic granules are almost always ○ Preoperative diphenhydramine 1 mg/kg
the cells (degranulation). Cytokine release present. IM (not IV)
produces clinical signs. Degranulation may • Before treatment: CBC, serum biochemistry ○ Wide surgical margins are not as important
be spontaneous or secondary to manipulation panel, urinalysis, and a regional lymph node in cats as in dogs because recurrence after
of the tumor. aspirate (if accessible) should be obtained. incomplete excision is uncommon in cats.
• MCTs may metastasize to regional LNs, ○ CBC: mastocythemia (mast cells in periph- ○ All tissue should be submitted for histo-
spleen, liver, bone marrow, mesenteric LNs, eral circulation), eosinophilia, basophilia, logic evaluation; margins should be inked
and skin. and regenerative or nonregenerative before placement in formalin.
• Feline leukemia virus and feline immuno- anemia are possible. Serum chemistry ○ Postoperative complications are uncom-
deficiency virus infections are not associated may be normal or reflect protein loss or mon; wound healing should be monitored
with the development of feline MCT. hepatic infiltration with mast cells. after resection of large, infiltrative MCTs.
○ LN aspirate and cytologic exams: normal; • MCTs in locations that may preclude
DIAGNOSIS LN may contain scattered mast cells; complete excision (i.e., periocular, pinna)
increased numbers or clusters of mast are common in cats. External beam RT (by
Diagnostic Overview cells in the LN draining an MCT suggest linear accelerator) is uncommonly used;
• Cutaneous MCT should be suspected in metastasis. strontium-90 plesiotherapy (radiation source
cats with small, white or pink, hairless, ○ Buffy coat smear: more specific in cats than applied directly to small tumors) may be
pimplelike lesions of the head and neck; dogs. A positive test supports a diagnosis used instead of or after marginal excision.
fine-needle aspiration (FNA) for cytologic of mastocytosis in cats with MCTs. • Chemotherapy and targeted therapy may play
exam is usually diagnostic. Cutaneous MCTs • Staging for systemic mast cell disease is a role in cats with multiple, nonresectable,
often temporarily bleed after aspiration. indicated before surgery in patients with or metastatic cutaneous MCTs.
• Any cat with splenomegaly should be lymph node metastasis, peritumoral edema Visceral (splenic or GI) forms:
suspected to have splenic MCT, and FNA or bruising, recurrent or multiple MCTs, • Take care not to excessively manipulate tumor
of the spleen should be considered. or if there is suspicion of splenic or visceral tissue because degranulation can result in
• GI MCT should be considered for any cat MCTs. anaphylaxis and hypotension. Perioperative
with an abdominal mass, although it is less ○ Staging includes the tests listed above diphenhydramine 1 mg/kg IM (not IV) and
common than other feline GI cancers. FNA plus thoracic radiographs (rare pleural possibly dexamethasone sodium phosphate
of the mass is usually diagnostic. effusion), abdominal ultrasound (LN, 1 mg/CAT IV (anecdotal) are recommended.

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