Transmissible venereal tumor
Transmissible venereal tumors (TVT) are contagious, sexually transmitted round cell neoplasm of dogs transmitted by direct contact with injured skin and/or mucous tissue. This disease is most common in sub-tropical and tropical urban regions of the world.
Epidemiological studies have shown that TVT show closely related histopathological characteristics and share common genetic alterations such as aneuploid karyotype with the presence of 58 to 59 chromosomes and a particular long interspersed nuclear element insertion near c-myc oncogene. Despite the common origin of TVT, tumor samples from different countries can be genetically subdivided, depending on their geographic origin.
This disease is transmitted between dogs via physical transfer of viable tumor cells. It is a spontaneous self-regression tumor whose behavior is closely related to host immune responses. Although TVT is mainly found in the sexual organs of female and male dogs, it can become highly invasive to other tissues, although metastasis occurs in low frequency.
They are usually seen in young, sexually active dogs from an environment with a high concentration of free roaming dogs with poor control of reproduction. Females are more susceptible than males, but there does not appear to be a breed predilection.
TVTs are transmitted by direct contact wherein viable tumor cells are seeded onto mucous membranes (especially when associated with trauma) or implanted subcutaneously in bite wounds. Due to their sexually transmitted nature they are most commonly found on the external genitalia. However, they also have been observed in other locations such as the nasal and oral cavities. In these instances the neoplasm is spread by social behaviors including sniffing and licking.
TVTs are single to multiple, pink-red, cauliflower-shaped lesions that can vary greatly in size. Neoplasms are relatively firm but fragile, especially those tumors involving the external genitalia. Because of a rich blood supply, TVTs appear pink to bright red. Hemorrhage is associated with tumor fragility. Other associated clinical signs may include genital discharge, abnormal odor, and excessive licking. If metastasis is present, local or distant lymphadenopathy may be observed.
Aspirates from TVTs are highly cellular and often bloody. Individual neoplastic cells have a round nucleus, fine to granular chromatin pattern, and often a single, prominent nucleolus. Mitotic figures are frequently observed. The cytoplasm is pale blue and moderately abundant. The most prominent cytological feature of TVTs is the presence of distinct, clear, cytoplasmic vacuoles.
TVT cells that lack cytoplasmic vacuoles may be easily confused with other round cell tumors. The morphological appearance and location of the tumor, however, are helpful in the diagnosis. A variety of inflammatory cells may be observed, especially in traumatized neoplasms.
The prognosis for TVTs is very good. Less than 5% of TVTs ultimately metastasize to other sites.
Even in the case of metastasis, the cure rate for TVTs is over 90%. Dogs generally tolerate vincristine administration well; fewer than 15% of treated dogs experience drug-related side effects.
Transmissible venereal tumors have also been shown to be very sensitive to radiation therapy.
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