Page 417 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 21 Mast Cell Tumors 395

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A B
• Fig. 21.9 (A) Multiple mast cell tumors on the head of a cat. The head and neck are the most commonly
encountered location for mast cell tumors in the cat. They often involve the area near the base of the
ear. (B) Mast cell tumors in the cat are less common on the limbs. (Courtesy S. Helfand, Oregon State
University.)

histiocytic form in young cats with multiple masses, as these may
spontaneously regress. 2,4,239
RT may be considered for tumors that are incompletely
excised. In one study of feline cutaneous MCT, a 98% control
rate was achieved with strontium-90 irradiation with an MST
greater than 3 years. 261 Limited information exists concerning
the utility of chemotherapy in cats with MCT. It is generally
believed that feline MCTs are less responsive to prednisone than
dogs; biologic activity of corticosteroids in cats with the histio-
cytic variant was found to be equivocal. 239 Objective responses to
lomustine (CCNU) have been reported in cats. 262,263 Of 20 cats
with cutaneous MCTs, two had a CR and eight cats had a PR
with lomustine. 263 The authors have observed evidence of clinical
activity in cats treated with prednisone and VBL. Some investiga-
tors have utilized a combination of prednisone and chlorambucil
• Fig. 21.10 Histiocytic mast cell tumors on the head of a young Siamese to treat metastatic or multiple tumors. This is generally well toler-
cat. This form of mast cell tumors in cats typically regress spontaneously, ated, although its effectiveness is not known.
as was the case in the cat pictured here. (Courtesy Dr. K. Moriello, Univer- Biologic activity of imatinib has been observed in cats with
sity of Wisconsin–Madison.) MCT expressing activating mutations in c-kit, although the
responses were all partial. 237,238,264 Studies in healthy cats have
surgical margins may not be as critical as in the dog. Frequency demonstrated that MAS may be safe to administer to clinically
of systemic spread after surgical excision varies from 0% to 22%, normal cats, and plasma concentrations associated with MCT
although those that metastasize are more likely to be anaplas- inhibitory activity are likely achievable. 265 Cats should be moni-
tic tumors. 244,245,247–249 Therefore for histologically anaplastic tored very closely for neutropenia, proteinuria, and increases
tumors or those with a high MI more likely recur postoperatively in creatinine. 266,267 TOC has been evaluated in multiple feline
or metastasize, a more aggressive approach similar to that used for tumor types, including MCT. Tolerability appears good at the
canine MCT may be prudent. 249,260 After biopsy confirmation, canine label dose and objective responses have been observed in
conservative resection or active surveillance may be taken with the some cats with MCTs. 268,269