Mast cell tumors are common tumors of the skin, intestinal tract, and spleen in cats.1 The biological behavior of MCTs in cats ranges from benign to malignant. Most cutaneous MCTs are benign, and recurrence or metastasis after excision or irradiation with radioactive strontium is rare.2-7 In contrast, most MCTs of the intestinal tract in cats are associated with a poor prognosis because of their infiltrative nature, tendency to cause adhesions, and high likelihood for regional and distant metastasis.8-12 Widespread dissemination and metastasis to the liver, visceral lymph nodes, bone marrow, and lung are common in cats with splenic MCTs.1 However, even in those cats with other evidence of systemic involvement, splenectomy in cats with splenic MCTs has been associated with long survival times, with 1 study13 reporting a median survival time of 19 months.
Surgery or radiation therapy is the most common treatment for cats with MCTs. Alternative systemic treatments, however, are needed for those cats in which surgery or radiation therapy is not possible or has not been successful (eg, cats with cutaneous or intestinal MCTs that are not resectable or are metastatic or recurrent). In addition, adjuvant systemic treatment might help improve tumor control and survival time following surgery in certain cats with MCTs, such as cats with intestinal MCTs that have undergone resection and cats with splenic MCTs that do not improve or have a recurrence after splenectomy To our knowledge, however, there have been no published studies evaluating response to various systemic treatments in cats with MCTs.
In dogs with measurable MCTs, lomustine is an effective systemic treatment, with an overall response rate of 42%.14 Acute neutropenia and hepatic damage are the principal toxic effects of lomustine in dogs.14-16 Other adverse effects documented uncommonly in dogs treated with lomustine include delayed and cumulative effects on the bone marrow,15 renal toxicosis,16 bicavi-tary effusion,16 and unexplained fever.15 In a phase I study to determine the maximum tolerated dose of lomustine and dose-limiting toxicoses associated with a single dose of lomustine in cats with various tumors, 1 cat with multiple cutaneous MCTs had a > 50% reduction in tumor burden.17 Neutropenia was concluded to be the acute dose-limiting adverse effect of lomustine in cats, and a dosage of 50 to 60 mg/m2 was recommended for future phase II trials.17 In another study18 3 cats with visceral MCTs were treated with lomustine but response could not be determined because only microscopic disease was present. A low incidence of myelo-suppression was reported in that study18 but because cats received a standard dose of lomustine (10 mg) regardless of body weight, the dosage of lomustine was < 50 mg/m2 in at least half of the 20 cats studied.
Taken together, these previous findings suggest that lomustine may be an effective systemic treatment for MCTs in cats. The purpose of the study reported here was to determine clinical activity and toxic effects of lomustine when used to treat cats with measurable MCTs.
Mast cell tumor
CeeNU, Bristol-Myers Squibb Co, Princeton, NJ.
Carpenter JL, Andrews LK, Holzworth J. Tumors and tumor-like lesions. In: Holzworth J, ed. Diseases of the cat: medicine and surgery. Philadelphia: WB Saunders, 1987;407–596.
Molander-McCrary H, Henry CJ, Potter K, et al. Cutaneous mast cell tumors in cats: 32 cases (1991–1994). J Am Anim Hosp Assoc 1998;34:281–284.
Johnson TO, Schulman FY, Lipscomb TP, et al. Histopathology and biologic behavior of pleomorphic cutaneous mast cell tumors in fifteen cats. Vet Pathol 2002;39:452–457.
Lepri E, Ricci G, Leonardi L, et al. Diagnostic and prognostic features of feline cutaneous mast cell tumours: a retrospective analysis of 40 cases. Vet Res Commun 2003;27(suppl 1):707–709.
Turrel JM, Farrelly J, Page RL, et al. Evaluation of strontium 90 irradiation in treatment of cutaneous mast cell tumors in cats: 35 cases (1992–2002). J Am Vet Med Assoc 2006;228:898–901.
Litster AL, Sorenmo KU. Characterisation of the signalment, clinical and survival characteristics of 41 cats with mast cell neoplasia. J Feline Med Surg 2006;8:177–183.
Peaston AE, Griffey SM. Visceral mast cell tumour with eosinophilia and eosinophilic peritoneal and pleural effusions in a cat. Aust Vet J 1994;71:215–217.
Howl JH, Petersen MG. Intestinal mast cell tumor in a cat: presentation as eosinophilic enteritis. J Am Anim Hosp Assoc 1995;31:457–461.
Slawienski MJ, Mauldin GE, Mauldin GN, et al. Malignant colonic neoplasia in cats: 46 cases (1990–1996). J Am Vet Med Assoc 1997;211:878–881.
Liska WD, MacEwen EG, Zaki FA, et al. Feline systemic mastocytosis: a review and results of splenectomy in seven cases. J Am Anim Hosp Assoc 1979;15:589–597.
Rassnick KM, Moore AS, Williams LE, et al. Treatment of canine mast cell tumors with CCNU (lomustine). J Vet Intern Med 1999;13:601–605.
Moore AS, London CA, Wood CA, et al. Lomustine (CCNU) for the treatment of resistant lymphoma in dogs. J Vet Intern Med 1999;13:395–398.
Kristal O, Rassnick KM, Gliatto JM, et al. Hepatotoxicity associated with CCNU (lomustine) chemotherapy in dogs. J Vet Intern Med 2004;18:75–80.
Rassnick KM, Gieger TL, Williams LE, et al. Phase I evaluation of CCNU (lomustine) in tumor-bearing cats. J Vet Intern Med 2001;15:196–199.
Fan TM, Kitchell BE, Dhaliwal RS, et al. Hematological toxicity and therapeutic efficacy of lomustine in 20 tumor-bearing cats: critical assessment of a practical dosing regimen. J Am Anim Hosp Assoc 2002;38:357–363.
Veterinary Co-operative Oncology Group. Veterinary Co-operative Oncology Group—common terminology criteria for adverse events (VCOG-CTCAE) following chemotherapy or biological antineoplastic therapy in dogs and cats v1.0. Vet Comp Oncol 2004;2:195–213.
Chu E, DeVita VT. Principles of cancer management: chemotherapy. In: DeVita VT, Hellman S, Rosenberg SA, eds. Cancer: principles and practice of oncology. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2001;289–306.
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.
Hanson JA, Papageorges M, Girard E, et al. Ultrasonographic appearance of splenic disease in 101 cats. Vet Radiol Ultrasound 2001;42:441–445.
Guerre R, Millet P, Groulade P. Systemic mastocytosis in a cat: remission after splenectomy. J Small Anim Pract 1979;20:769–772.