Overview and Transmission
Cancer in humans is practically never transmitted from one person to another. Only very rare documented exceptions exist, usually involving surgical mishaps. Sticker's sarcoma or Canine Transmissible Venereal Tumor (CTVT) is a very unusual form of cancer affecting canines (i.e. dogs). CTVT is transmitted by mating, licking, or other direct contact.1 The tumor affects the genitalia. In some cases the urethra becomes blocked making it difficult for the affected animal to urinate.2 The image below (left) is of a CTVT tumor, showing a typical 'cauliflower-like' mounds. The second image below (right) is a view of CTVT cancer cells as seen in a microscope. If the cancer is located at the mouth and nose, nosebleeds, facial swelling, and nostril discharge are common symptoms.
Many human cancers are caused by viruses, including the human papilloma virus (HPV), a major cause of cervical cancer. Infection with viruses can lead to changes in normal cells within the infected person and lead to the development of cancer. CTVT is different! In this case, the cancer cells themselves are transmitted from animal to animal. Once in the new animal, the tumor can grow and eventually be spread to additional animals.3 Experiments have shown that CTVT is not transmissible via killed tumor cells or by cell contents.1 Viruses are usually present in a cell's liquid contents; if the liquid contents do not transfer CTVT, it is evidence that viruses are not responsible for the cancer. Also, all tumor cells examined so far have a molecular "fingerprint" in their DNA that is absent in normal cells. Specifically, the cancer cells contain a DNA sequence called Line-1 inserted near the oncogene c-myc.4
Researchers have compared tumor DNA and normal DNA within different breeds of dogs. The results showed the expected differences between the normal cell DNA, but all tumor DNA samples were very similar despite being from very different dogs. These results indicate that the tumor cells themselves transfer CTVT between animals.3
In most cases, the immune system recognizes and eliminates cells of other types that are introduced into an animal (or human). This does not happen with CTVT. Upon the initial infection, CTVT begins a state of rapid and intense growth that lasts anywhere from three to nine months and possibly longer in old or weakened dogs.1 This is usually followed by a variable regression phase.
Treatment for CTVT
Treatment choices for CTVT include surgery, chemotherapy, or radiation therapy. Chemotherapy is often very effective, usually resulting in complete remission. Surgery does not have a similarly high success rate.5Because the cancer is transmitted between animals and across generations, the cancer itself is thought to be very old! CTVT is thought to be anywhere from 200-2500 years old and represents the longest line of unbroken replications of a mammal's body cell. Aside from domesticated dogs, it is also transmissible to coyotes, foxes, jackals, wolves and immuno-suppressed mice.16
CTVT is not transmissible to humans!
- 1. a. b. c. d. Cohen, D. (1985). The canine transmissible venereal tumor: a unique result of tumor progression. Adv. Cancer Res. 43, 75112. [PUBMED]
- 2. Hasler A, Weber W (2000). "Theriogenology question of the month. Transmissible venereal tumor (TVT)." J. Am. Vet. Med. Assoc. 216 (10): 15579. [PUBMED]
- 3. a. b. Murgia C, Pritchard JK, Kim SY, Fassati A, Weiss RA. "Clonal Origin and Evolution of a Transmissible Cancer". Cell (2006) 126(3):47787. doi:10.1016/j.cell.2006.05.051. [PUBMED]
- 4. Katzir N, Rechavi G, Cohen JB, Unger T, Simoni F, Segal S, Cohen D, Givol D. "Retroposon" insertion into the cellular oncogene c-myc in canine transmissible venereal tumor. Proc. Natl. Acad. Sci. USA (1985) 82, 10541058. [PUBMED]
- 5. Ettinger, Stephen J; Feldman, Edward C. (1995). Textbook of Veterinary Internal Medicine (4th ed.). W.B. Saunders Company. ISBN 0-7216-6795-3. [http://en.wikipedia.org/w/index.php?title=Special%3ABookSources&isbn=0721667953]
- 6. Harmelin A, Pinthus JH, Katzir N, Kapon A, Volcani Y, Amariglio EN, Rehavi G. (2001). "Use of a murine xenograft model for canine transmissible venereal tumor." Am. J. Vet. Res. 62, 907911. [PUBMED]