Transmissible venereal tumor

From Dog
Transmissible venereal tumor in a bitch[1]
Transmissible venereal tumor in a bitch[2]
Transmissible venereal tumor in a dog[3]

Transmissible venereal tumors (TVT) are contagious, sexually transmitted round cell neoplasm of dogs transmitted by direct contact with injured skin and/or mucous tissue[4]. 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[5]. 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[6]. It is a spontaneous self-regression tumor whose behavior is closely related to host immune responses[7]. 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[8].

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[9], but there does not appear to be a breed predilection.

This disease is enzootic in many areas of the world including the southern United States[10] and appears to be more aggressive with dogs concurrently infected with Leishmania donovani[11].

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[12].

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[13].

Vincristine or combined BCG and vincristine therapy are the treatments of choice[14], with the majority of dogs being cured[15].

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.

For tumors that are resistant to vincristine, doxorubicin or doxil should be considered alternative chemotherapeutic agents.

Transmissible venereal tumors have also been shown to be very sensitive to radiation therapy.

References

  1. Access Science
  2. Pholae Vet Clinic
  3. Uni of Pennsylvania
  4. Stockmann D et al (2011) Detection of the tumour suppressor gene TP53 and expression of p53, Bcl-2 and p63 proteins in canine transmissible venereal tumour. Vet Comp Oncol 9(4):251-259
  5. Liao KW et al (2003) Identification of canine transmissible venereal tumor cells using in situ polymerase chain reaction and the stable sequence of the long interspersed nuclear element. J Vet Diagn Invest 15:399–406
  6. Murchison EP (2008) Clonally transmissible cancers in dogs and Tasmanian devils. Oncogene 27(2):S19-S30
  7. Pai CC et al (2011) Immunopathogenic behaviors of canine transmissible venereal tumor in dogs following an immunotherapy using dendritic/tumor cell hybrid. Vet Immunol Immunopathol 139(2-4):187-199
  8. Calvert CA et al (1982) Vincristine for treatment of transmissible venereal tumor in the dog. J Am Vet Med Assoc 181:163–164
  9. Kabuusu RM et al (2010) Risk factors and characteristics of canine transmissible venereal tumours in Grenada, West Indies. Vet Comp Oncol 8(1):50-55
  10. Rogers KS. (1997) Transmissible venereal tumor. Compend Contin Educ Pract Vet 19:1036-1045
  11. Marino G et al (2012) Clinicopathological study of canine transmissible venereal tumour in leishmaniotic dogs. J Small Anim Pract 53(6):323-327
  12. Duncan JR, Prasse KW. (1979) Cytology of canine cutaneous round cell tumors. Vet Pathol 16:673-679
  13. Meleo KA. (1997) Tumors of the skin and associated structures. Vet Clin N Amer 27:73-94
  14. Mukaratirwa S et al (2009) Combination therapy using intratumoral bacillus Calmette-Guerin (BCG) and vincristine in dogs with transmissible venereal tumours: therapeutic efficacy and histological changes. J S Afr Vet Assoc 80(2):92-96
  15. Özalp GR et al (2012) Vincristine modulates the expression of Ki67 and apoptosis in naturally occurring canine transmissible venereal tumor (TVT). Biotech Histochem 87(5):325-330