Small Animal Dermatology, 3rd edition

CHAPTER 33 MAST CELL TUMORS 499

Cyclophosphamide: 250–300 mg/m^2 PO divided over 4 days; administer on days

8, 9, 10, and 11 of each 21-day cycle; initiate at 250 mg/m^2 for two cycles;

increase to 300 mg/m^2 for cycle 3 if well tolerated; continue for 6 months

Lomustine (CCNU): 50–70 mg/m^2 PO q21 days

Toceranib phosphate: 2.75 mg/kg PO M/W/F; tyrosine kinase inhibitor; also

targets vascular endothelial growth factor receptor 2, and PDGFR-beta 42.8%

response rate; median time to progression 126 days

Mastinib 12.5 mg/kg PO q24h; tyrosine kinase inhibitor; also targets platelet-

derived growth factors alpha and beta, and fibroblast growth factor 3; overall

response 82.1%; median time to progression 79 days.

 Cats:

Lomustine 32–60 mg/m (^2) PO q4–6 weeks
Vinblastine 2 mg/kg/m (^2) IV q7 days for four treatments; then q14 days with pred-
nisolone 1 mg/kg PO q24h.
 Histamine-blocking agents (e.g., cimetidine): helpful for systemic mastocytosis or
when massive histamine release is of concern; helps to prevent gastric ulceration and
counteract negative effects of histamine on fibroplasia in wound healing.
 Sucralfate helpful if gastrointestinal ulceration present: binds to ulcer site.
 Prednisolone-resistant tumor: chemotherapy does not appear to be beneficial.
 Intestinal tumor and systemic mastocytosis after splenectomy (cats): prednisolone
and chemotherapy indicated.
 Vinblastine and lomustine: myelosuppressive; use with caution in patients with liver
disease.
 Toceranib and mastinib: use with caution with other drugs that may induce gastric
ulceration.
COMMENTS
Client Education/Patient Monitoring
 Warn client that a patient that has had more than one cutaneous tumor is predisposed
to developing new mast cell tumors.
 Advise client that fine-needle aspiration and cytologic examination should be per-
formed as soon as possible on any new mass.
 Inform client that appropriate surgical excision should be done as soon as possible.
 Evaluate any new masses cytologically or histologically.
 Evaluate regional lymph nodes at regular intervals to detect metastasis of grade 2 or
3 tumor.
Expected Course and Prognosis
 Dogs:
Tumors in the inguinal region: tend to be more aggressive than similarly graded
tumors in other locations; always considered to have the potential to metastasize