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
This article highlights the distinguishing cytologic characteristics of canine 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.
This case report was provided by Rob Simoni, DVM, and Joyce S. Knoll, VMD, PhD, DACVP, Department of Biomedical Sciences,
Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.
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