Page 806 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

784 PART IV Specific Malignancies in the Small Animal Patient

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• Fig. 34.7 Other primary tumor sites. (A) Male dog with cutaneous dissemination of transmissible venereal
tumor (TVT) on the ventral abdomen. (B) Mucocutaneous TVT of the anal area in a dog. (C) Corneal involve-
ment with TVT in a dog. (Courtesy Pr. Noeme S. Rocha.)

can be difficult to obtain wide surgical margins in the areas in
which TVT typically appears. 248,250,251 In addition, tumor trans- SECTION D: MESOTHELIOMA
plantation into the surgical wound by contamination from instru-
ments or gloves may also cause postoperative tumor recurrence.
Other therapies described in spontaneous and experimentally LAURA D. GARRETT
induced cases include biologic-response modifiers (IL-2), piroxi-
cam, cryosurgery, radiofrequency ablation, laser ablation, and Incidence and Risk Factors
electrochemotherapy. 252–257
Reduction of the incidence of TVT is possible by having dog Mesothelioma is a rare neoplasm of dogs and cats affecting the
owners and breeders carefully examine all males and females cells lining the coelomic cavities of the body. In 1962, Gerb
before mating to avoid breeding affected animals. 186 In addition, et al cited reports of one case of mesothelioma in 1000 dogs and
stray dogs can act as a TVT reservoir; therefore the mingling of three cases in 5315 dogs. 258 In dogs, primary mesothelial tumors
breeding dogs with strays should be prevented. In some areas, affecting the thoracic cavity, abdominal cavity, pericardial sac,
the control of ownerless, free-roaming dogs can drastically reduce and vaginal tunics of the scrotum have been reported. 259–264 In
the incidence of TVT. TVT can enter the wild canid population the cat, primary mesotheliomas have been reported in the peri-
through physical contact, and it is not known whether TVT may cardium, pleura, and peritoneum, as well as throughout the abdo-
pose a threat to endangered wild canids. 205 men, with lung and mediastinal lymph node metastases. 265–270
Exposure to asbestos may be an important contributory factor
Prognosis to mesothelioma development in pet dog populations. Affected
dogs often have owners who have jobs or hobbies for which
In most cases, TVT remains localized and rarely becomes dissemi- exposure to asbestos is a known risk. 271 The level of asbestos in
nated, with some dogs having spontaneous regression. For those lung tissues of affected dogs has been documented to be greater
dogs requiring treatment with vincristine or RT, the prognosis than in controls. 271,272 Asbestos refers to a family of silicate min-
for complete and durable clinical remission is excellent. There- erals that crystallize into long, flexible fibers. The fibers are cate-
fore the overall prognosis of canine TVT is generally very good gorized into two groups: thin rodlike amphiboles, and long curly
to excellent. serpentine, the main type being chrysotile. In humans, much