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Canine transmissible venereal tumor:
Canine transmissible venereal tumor cytology

Canine transmissible venereal tumor (CTVT), also called transmissible venereal tumor (TVT), Sticker tumor and infectious sarcoma is a histiocytic tumor of the dog and other canids that mainly affects the external genitalia, and is transmitted from animal to animal during copulation.

Contents

[edit] History

Canine TVT was initially described by Russian veterinarian M.A. Novinsky (1841–1914) in 1876, when he demonstrated that the tumor could be transplanted from one dog to another by infecting them with tumor cells.[1]

It has been proposed that the tumor cells responsible for canine transmissible venereal tumor be considered a parasitic cancer. It has been estimated that the tumour cell line originated 200 to 2,500 years ago in a wolf, coyote, or old Asian dog breed such as a Husky or Shih Tzu. The tumour cells are themselves the infectious agents. [2][3]

[edit] Biology

CTVT is a histiocytic tumor that may be transmitted among dogs through coitus, licking, biting and sniffing tumor affected areas. The concept that the tumor is naturally transmissible as an allograft came from three important observations. First, CTVT can only be experimentally induced by transplanting living tumor cells, and not by killed cells or cell filtrates. Second, the tumor karyotes is aneuploid but has characteristic marker chromosomes in all tumors collected in different geographic regions. Third, a long interspresed nuclear element (LINE-1) insertion near c-myc has been found in all tumors examined so far and can be used as a diagnostic marker to confirm that a tumor is CTVT.[4]

CTVT cells have fewer chromosomes than normal cells. Dog cells normally have 78 chromosomes; CTVT tumor cells contain 57–64 chromosomes[1] that are very different in appearance from normal dog chromosomes. All dog chromosomes except X and Y are acrocentric, having a centromere very near to the end of the chromosome, while many of the CTVT chromosomes are metacentric or submetacentric, having a centromere nearer to the middle.[5] There is no evidence that the tumor is caused by a virus or virus-like organism. The infectious agent of canine transmissible venereal tumor is the cancer cell itself and that the tumor is clonal in origin. All tumor cells of this type of cancer share extremely similar genetic code, often if not always unrelated to the DNA of their host. Specifically, the LINE-1 (Long interspersed nuclear element) element in the tumor cells is in a different location than in normal canine DNA.[4] This demonstrates that the tumors do not arise from separate cancerous transformation in individual animals. Rather, the malignant tumor cells from one dog are transferred to another dog via coitus, licking, biting, and sniffing tumor-affected areas. [6][7]

CTVT is most commonly seen in sexually active dogs in tropical and subtropical climates. The disease is spread when dogs mate, and it can even be transmitted to other canine species, such as foxes and coyotes.[8] Spontaneous regression of the tumor can occur, probably due to a response from the immune system.[9] CTVT undergoes a predictable cycle: the initial growth phase of four to six months (P phase), a stable phase, and a regression phase (R phase),[10] although not all CTVTs will regress. The tumor does not often metastasize (occurring in about 5 percent of cases),[11] except in puppies and immunocompromised dogs. Metastasis is most commonly to regional lymph nodes, but can also be seen in the skin, brain, eye, liver, spleen, testicle, and muscle.[12] Biopsy is necessary for diagnosis.

The success of this single cell lineage, believed to be the longest continually propagated cell lineage in the world, can be attributed to the tumor’s mode of transmission in a specific host system. Although direct contact is generally not a highly efficient mode of transfer, CTVT takes advantage of the “popular sire” effect of domestic dogs. A single male can produce dozens of litters over his lifetime, allowing the tumor to affect many more females than it could if a monogamous species were the host. Understanding the epidemiology of CTVT will provide insights for populations that may experience CTVT exposure and information about disease prevalence. CTVT is more often found in temperate climates where there are large populations of stray dogs, but little is known about the details of transmission.[13]

[edit] Signs and symptoms

In male dogs, the tumor affects the penis or prepuce. In females, it affects the vagina or labia. Rarely, the mouth or nose are affected.[14] The tumor often has a cauliflower-like appearance. Signs of genital TVT include a discharge from the prepuce and in some cases urinary retention, from blockage of the urethra.[5] Signs of nasal TVT include oronasal fistulae, nosebleeds and other nasal discharge, facial swelling, and enlargement of the submandibular lymph nodes.[15]

[edit] Treatment

Chemotherapy is very effective for TVT, but surgery alone often leads to recurrence. Surgery may be difficult due to the location of these tumors. The prognosis for complete remission with chemotherapy is excellent.[16] The most common chemotherapy agents used for TVT are vincristine, vinblastine, and doxorubicin.[9] Radiation therapy may be effective when chemotherapy does not work.[12]

[edit] References

  1. ^ a b Mello Martins, M.I.; de Souza, F. Ferreira; Gobello, C. (2005). "Canine transmissible venereal tumor: Etiology, pathology, diagnosis and treatment". Recent Advances in Small Animal Reproduction. Retrieved on 2006-05-25.
  2. ^ Murgia, C; Pritchard JK, Kim SY, Fassati A, Weiss RA (2006-08-11). "Clonal Origin and Evolution of a Transmissible Cancer". Cell 126 (3): 477–87. doi:10.1016/j.cell.2006.05.051. PMID 16901782. 
  3. ^ Choi, Charles Q. (2006-08-10). "Contagious Canine Cancer Spread by Parasites". LiveScience. Retrieved on 2006-08-11.
  4. ^ a b Murgia, et al.; (2006). "Clonal Origin and Evolution of a Transmissible Cancer". Cell 126: 477–487. doi:10.1016/j.cell.2006.05.051. PMID 16901782. 
  5. ^ a b Hasler A, Weber W (2000). "Theriogenology question of the month. Transmissible venereal tumor (TVT)". J. Am. Vet. Med. Assoc. 216 (10): 1557–9. PMID 10825939. 
  6. ^ Murgia C, Pritchard JK, Kim SY, Fassati A, Weiss RA. Clonal origin and evolution of a transmissible cancer. Cell. 2006 Aug 11;126(3):477-87.
  7. ^ Dingli D, Nowak MA. Cancer biology: infectious tumour cells. Nature. 2006 Sep 7;443(7107):35-6. B).
  8. ^ Mukaratirwa S, Gruys E (2003). "Canine transmissible venereal tumour: cytogenetic origin, immunophenotype, and immunobiology. A review". The Veterinary quarterly 25 (3): 101–11. PMID 14535580. 
  9. ^ a b Stettner N, Brenner O, Eilam R, Harmelin A (2005). "Pegylated liposomal doxorubicin as a chemotherapeutic agent for treatment of canine transmissible venereal tumor in murine models". J. Vet. Med. Sci. 67 (11): 1133–9. doi:10.1292/jvms.67.1133. PMID 16327225. 
  10. ^ Liao K, Hung S, Hsiao Y, Bennett M, Chu R (2003). "Canine transmissible venereal tumor cell depletion of B lymphocytes: molecule(s) specifically toxic for B cells". Vet. Immunol. Immunopathol. 92 (3–4): 149–62. doi:10.1016/S0165-2427(03)00032-1. PMID 12730015. 
  11. ^ "Canine Transmissible Venereal Tumor: Introduction". The Merck Veterinary Manual (2006). Retrieved on 2007-04-24.
  12. ^ a b Rogers K, Walker M, Dillon H (1998). "Transmissible venereal tumor: a retrospective study of 29 cases". Journal of the American Animal Hospital Association 34 (6): 463–70. PMID 9826280. 
  13. ^ Bridgett M. vonHoldt and Elaine A. Ostrander. The Singular History of a Canine Transmissible Tumor. Cell. 126. 2006.
  14. ^ Morrison, Wallace B. (1998). Cancer in Dogs and Cats (1st ed.). Williams and Wilkins. ISBN 0-683-06105-4. 
  15. ^ Papazoglou L, Koutinas A, Plevraki A, Tontis D (2001). "Primary intranasal transmissible venereal tumour in the dog: a retrospective study of six spontaneous cases". Journal of veterinary medicine. A, Physiology, pathology, clinical medicine 48 (7): 391–400. PMID 11599677. 
  16. ^ Ettinger, Stephen J.;Feldman, Edward C. (1995). Textbook of Veterinary Internal Medicine (4th ed.). W.B. Saunders Company. ISBN 0-7216-6795-3. 

[edit] External links

[edit] See also

  • Devil facial tumour disease — a similarly transmissible "immortal cell" cancer in the Tasmanian Devil.
  • HeLa cells — immortal cell line used in biomedical research
Retrieved from "http://en.wikipedia.org/wiki/Canine_transmissible_venereal_tumor"



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