Veterinary Medicine - June 2008 - (Page 304)

Clinical Exposures PEER-REVIEWED 5A. A ﬁne-needle aspirate from a cutaneous mast cell tumor in a dog. Note the well-differentiated mast cells with numerous distinct metachromatic granules in the cytoplasm, sometimes obscuring the nucleus (Wright’s-Giemsa stain; 100X). 5B. A ﬁne-needle aspirate of a cutaneous melanoma in a dog. Note the welldifferentiated melanocytes with numerous ﬁne green-black melanin granules in the cytoplasm. The nuclei are round to irregularly round with coarse chromatin and one or two nucleoli. Numerous free granules and some red blood cells are present in the background (Wright’s-Giemsa stain; 100X). 6. A ﬁne-needle aspirate from a cutaneous mass in a dog revealing a poorly granulated mast cell tumor. These cells are round with sharply deﬁned cell margins, pale cytoplasm, and nuclei that are central to slightly offset, giving them a fried egg appearance. The cytoplasm is much lighter than that of other tumor types, with a scattering of metachromatic granules (difﬁcult to see in this view) that help to conﬁrm these as mast cells (Wright’s-Giemsa stain; 100X). role in inhibiting the growth and spread of the neoplasm.3 Similar to observations in histiocytomas, increased lymphocytes and plasma cells may be observed cytologically on impression smears and aspirates in regressing tumors, compared with progressing tumors.3 Therapy and prognosis In animals that have an appropriate antitumor immunologic response, spontaneous tumor regression may occur after the tumor reaches a certain size. However, in animals that are unable to mount an appropriate immunologic response, the tumor may continue to grow and metastasize.3 Therapy is generally recommended when a canine transmissible venereal tumor is deﬁnitively diagnosed. Several therapeutic modalities have been used with canine transmissible venereal tumors, including surgery, radiation therapy, biologic response modiﬁers (experimentally), and chemotherapy.3 The goal of biologic response modiﬁers, or biotherapy, is to alter the tumor-host relationship by acting on the host immune system or by directly affecting tumor cells or their microenvironment. Examples include tumor antigen vaccines, nonspeciﬁc immunomodulators, or growth factors.3 Surgery may be effective for small and localized cutaneous nodules, although adequate excision is usually not possible when external genitalia are involved, and the recurrence rate in these instances varies from 20% to 60%.3 Radiation therapy has also been effective.3 Chemotherapy is the most effective way to treat canine transmissible venereal tumor.3 Various chemotherapeutic agents such as vincristine, cyclophosphamide, doxorubicin, and methotrexate have been used, and vincristine is considered one of the most effective agents.3 It typically takes four to six once-weekly treatments (possibly more) to induce complete remission, and a complete cure can be expected in more than 90% of patients treated with this protocol.3 transmissible venereal tumors. History, signalment, and tumor location can also be important factors in diagnosing canine transmissible venereal tumors. Your index of suspicion should be high in intact, sexually active dogs that are allowed to roam, especially those living in or that have visited temperate climates. Clinical signs, signalment, and cytologic features are often sufﬁcient for making this diagnosis. Biopsy and histologic examination are not necessary except in those cases with an atypical presentation. REFERENCES 1. VonHoldt BM, Ostrander, EA. The singular history of a canine transmissible tumor. Cell 2006;126(3):445-447. 2. Murgia C, Pritchard JK, Kim SY, et al. Clonal origin and evolution of a transmissible cancer. Cell 2006;126(3);477-487. 3. MacEwen G. Transmissible venereal tumor. In: Small animal clinical oncology. 3rd ed. Philadelphia, Pa: WB Saunders Co, 2001;651-655. 4. Marcos R, Santos M, Marrinhas C, et al. Cutaneous transmissible venereal tumor without genital involvement in a prepubertal female dog. Vet Clin Pathol 2006;35(1):106-109. 5. Henson KL. Reproductive system. In: Atlas of canine and feline cytology. Philadelphia, Pa: WB Saunders Co, 2001;296-297. 6. Goldschmidt MH, Hendrick, MJ. Tumors of the skin and soft tissues. In: Tumors in domestic animals. 4th ed. Ames: Iowa State Press, 2002;115-117. 7. Zinkl JG. Cytology of the male reproductive tract. In: Diagnostic cytology and hematology of the dog and cat. St. Louis, Mo: Mosby Inc, 1999;236-237. CONCLUSION This article highlights the distinguishing cytologic characteristics of canine 304 June 2008 VETERINARY MEDICINE

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Veterinary Medicine - June 2008 Contents Leading Off Clinical Exposures Idea Exchange A Challenging Case: Conjunctival Lymphoma in a Cat Updates on Canine Hypoadrenocorticism Product Preview CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller Clinical Edge - June 2008 Table of Contents Managing Diabetes Mellitus in Cats: What Makes it Work? Porcine Insulin Zinc Suspension in the Management of Feline Diabetes Mellitus Monitoring Diabetes Mellitus in Diabetic Cats Feline Diabetes Mellitus: Important Client Communication Points

Veterinary Medicine - June 2008

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