A canine transmissible venereal tumor (CTVT), also known as a transmissible venereal tumor (TVT), canine transmissible venereal sarcoma (CTVS), sticker tumor and infectious sarcoma, is a histiocytic tumor of the external genitalia of the dog and other canines, and is transmitted from animal to animal during mating. It is one of only three known transmissible cancers in mammals; the others are devil facial tumor disease, a cancer which occurs in Tasmanian devils, and contagious reticulum cell sarcoma of the Syrian hamster.
The tumor cells are themselves the infectious agents, and the tumors that form are not genetically related to the host dog. [1] Although the genome of a CTVT is derived from an individual canid (specifically from a population of Native American dogs with coyote contribution), [2] [3] it is now essentially living as a unicellular, asexually reproducing (but sexually transmitted) pathogen. [4] Sequence analysis of the genome suggests it diverged from canids over 6,000 years ago; possibly much earlier. [4] Estimates from 2015 date its time of origin to about 11,000 years ago. [5] However, the most recent common ancestor of extant tumors is more recent: it probably originated 200 to 2,500 years ago. [1] [6]
Canine TVTs were 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. [7]
In male dogs, the tumor affects the penis and foreskin. In female dogs, it affects the vulva. Rarely, the mouth or nose are affected. [8] The tumor often has a cauliflower-like appearance. Signs of genital TVT include a discharge from the prepuce and in some cases urinary retention caused by blockage of the urethra. [9] Signs of a nasal TVT include nasal fistulae, nosebleeds and other nasal discharge, facial swelling, and enlargement of the submandibular lymph nodes. [10]
Canine transmissible venereal tumors are histiocytic tumors 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, CTVTs can only be experimentally induced by transplanting living tumor cells, and not by killed cells or cell filtrates. Second, the tumor karyotype is aneuploid but has characteristic marker chromosomes in all tumors collected in different geographic regions. Third, a long interspersed nuclear element (LINE-1) insertion near the c-myc gene has been found in all tumors examined so far and can be used as a diagnostic marker to confirm that a tumor is a CTVT. [6] [11]
Canine transmissible venereal tumors are most commonly seen in sexually active dogs in tropical, subtropical and temperate climates where there are large populations of stray dogs, but little is known about the details of transmission. [12] The disease is spread when dogs mate, and can even be transmitted to other canine species, such as foxes and coyotes. [13] Spontaneous regression of the tumor can occur, probably due to a response from the immune system. [14] CTVT undergoes a predictable cycle: an initial growth phase of four to six months (P phase), a stable phase, and a regression phase (R phase), [15] although not all CTVTs will regress. The tumor does not often metastasize (occurring in about less than 5 percent of cases), [16] except in puppies and immunocompromised dogs. Metastasis occurs to regional lymph nodes,[ citation needed ] but can also be seen in the skin, brain, eye, liver, spleen, testicle, rectum and muscle. [17] A 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, CTVTs take 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 CTVTs could provide insights for populations that may experience CTVT exposure and information about disease prevalence.[ citation needed ]
The CTVT cells have fewer chromosomes than normal dog cells. Dog cells normally have 78 chromosomes, while the cancer cells contain 57–64 chromosomes [7] 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. [9]
All tumor cells of this type of cancer share extremely similar genetic code, often if not always unrelated to the DNA of their host. [6] In addition to the aforementioned c-myc insertion, a few other potential driver mutations have been identified. [18]
The tumor, when treated with the chemotherapy drug vincristine, regresses as the host immune system is activated. CCL5 may play an important role in the immune response. [19]
Surgery may be difficult due to the location of these tumors. Surgery alone often leads to recurrence. Chemotherapy is very effective for TVTs. The prognosis for complete remission with chemotherapy is excellent. [20] The most common chemotherapy agents used are vincristine, vinblastine, and doxorubicin. [14] Use of autohaemotherapy in treatment of TVTs also showed promising results in many cases [21] .Radiotherapy may be required if chemotherapy does not work. [17]
An osteosarcoma (OS) or osteogenic sarcoma (OGS) is a cancerous tumor in a bone. Specifically, it is an aggressive malignant neoplasm that arises from primitive transformed cells of mesenchymal origin and that exhibits osteoblastic differentiation and produces malignant osteoid.
Hemangiosarcoma is a rapidly growing, highly invasive variety of cancer that occurs almost exclusively in dogs, and only rarely in cats, horses, mice, or humans. It is a sarcoma arising from the lining of blood vessels; that is, blood-filled channels and spaces are commonly observed microscopically. A frequent cause of death is the rupturing of this tumor, causing the patient to rapidly bleed to death.
James Stephen Ewing was an American pathologist. He was the first professor of pathology at Cornell University and discovered a form of bone cancer that was later named after him, Ewing sarcoma.
Fibrosarcoma is a malignant mesenchymal tumour derived from fibrous connective tissue and characterized by the presence of immature proliferating fibroblasts or undifferentiated anaplastic spindle cells in a storiform pattern. Fibrosarcomas mainly arise in people between the ages of 25 and 79. It originates in fibrous tissues of the bone and invades long or flat bones such as the femur, tibia, and mandible. It also involves the periosteum and overlying muscle.
A synovial sarcoma is a rare form of cancer which occurs primarily in the extremities of the arms or legs, often in proximity to joint capsules and tendon sheaths. It is a type of soft-tissue sarcoma.
Devil facial tumour disease (DFTD) is an aggressive non-viral clonally transmissible cancer which affects Tasmanian devils, a marsupial native to the Australian island of Tasmania. The cancer manifests itself as lumps of soft and ulcerating tissue around the mouth, which may invade surrounding organs and metastasise to other parts of the body. Severe genetic abnormalities exist in cancer cells—for example, DFT2 cells are tetraploid, containing twice as much genetic material as normal cells. DFTD is most often spread by bites, when teeth come into contact with cancer cells; less important pathways of transmission are ingesting of infected carcasses and sharing of food. Adult Tasmanian devils who are otherwise the fittest are most susceptible to the disease.
Desmoplastic small-round-cell tumor (DSRCT) is an aggressive and rare cancer that primarily occurs as masses in the abdomen. Other areas affected may include the lymph nodes, the lining of the abdomen, diaphragm, spleen, liver, chest wall, skull, spinal cord, large intestine, small intestine, bladder, brain, lungs, testicles, ovaries, and the pelvis. Reported sites of metastatic spread include the liver, lungs, lymph nodes, brain, skull, and bones. It is characterized by the EWS-WT1 fusion protein.
Lymphoma (lymphosarcoma) in animals is a type of cancer defined by a proliferation of malignant lymphocytes within solid organs such as the lymph nodes, bone marrow, liver and spleen. The disease also may occur in the eye, skin, and gastrointestinal tract.
A mammary tumor is a neoplasm originating in the mammary gland. It is a common finding in older female dogs and cats that are not spayed, but they are found in other animals as well. The mammary glands in dogs and cats are associated with their nipples and extend from the underside of the chest to the groin on both sides of the midline. There are many differences between mammary tumors in animals and breast cancer in humans, including tumor type, malignancy, and treatment options. The prevalence in dogs is about three times that of women. In dogs, mammary tumors are the second most common tumor over all and the most common tumor in female dogs with a reported incidence of 3.4%. Multiple studies have documented that spaying female dogs when young greatly decreases their risk of developing mammary neoplasia when aged. Compared with female dogs left intact, those spayed before puberty have 0.5% of the risk, those spayed after one estrous cycle have 8.0% of the risk, and dogs spayed after two estrous cycles have 26.0% of the risk of developing mammary neoplasia later in life. Overall, unspayed female dogs have a seven times greater risk of developing mammary neoplasia than do those that are spayed. While the benefit of spaying decreases with each estrous cycle, some benefit has been demonstrated in female dogs even up to 9 years of age. There is a much lower risk in male dogs and a risk in cats about half that of dogs.
A histiocytoma in the dog is a benign tumor. It is an abnormal growth in the skin of histiocytes (histiocytosis), a cell that is part of the immune system. A similar disease in humans, Hashimoto-Pritzker disease, is also a Langerhans cell histiocytosis. Dog breeds that may be more at risk for this tumor include Bulldogs, American Pit Bull Terriers, American Staffordshire Terriers, Scottish Terriers, Greyhounds, Boxers, and Boston Terriers. They also rarely occur in goats and cattle.
A transmissible cancer is a cancer cell or cluster of cancer cells that can be transferred between individuals without the involvement of an infectious agent, such as an oncovirus. The evolution of transmissible cancer has occurred naturally in other animal species, but human cancer transmission is rare. This transfer is typically between members of the same species or closely related species.
Ewing sarcoma is a type of pediatric cancer that forms in bone or soft tissue. Symptoms may include swelling and pain at the site of the tumor, fever, and a bone fracture. The most common areas where it begins are the legs, pelvis, and chest wall. In about 25% of cases, the cancer has already spread to other parts of the body at the time of diagnosis. Complications may include a pleural effusion or paraplegia.
Cancer is the leading cause of death in dogs. It is estimated that 1 in 3 domestic dogs will develop cancer, which is the same incidence of cancer among humans. Dogs can develop a variety of cancers and most are very similar to those found in humans. Dogs can develop carcinomas of epithelial cells and organs, sarcomas of connective tissues and bones, and lymphomas or leukemias of the circulatory system. Selective breeding of dogs has led certain pure-bred breeds to be at high-risk for specific kinds of cancer.
Electrochemotherapy (ECT) is a type of chemotherapy that allows delivery of non-permeant drugs to the cell interior. It is based on the local application of short and intense electric pulses that transiently permeabilize the cell membrane, thus allowing transport of molecules otherwise not permitted by the membrane. Applications for treatment of cutaneous and subcutaneous tumors have reached clinical use by utilizing drugs such as bleomycin or cisplatin). Electrochemotherapy with bleomycin was used to treat a patient for the first time in 1991 at the Institute Gustave Roussy in France, while electrochemotherapy with cisplatin was used to treat for the first time in 1995 at the Institute of Oncology, Ljubljana, Slovenia. Since then, more than 4000 patients were treated with electrochemotherapy all over the world. Recently, new electrochemotherapy modalities have been developed for treatment of internal tumors using surgical procedures, endoscopic routes, or percutaneous approaches to gain access to the treatment area.
Elizabeth Murchison is a British-Australian geneticist, Professor of Comparative Oncology and Genetics at the University of Cambridge, UK. The ongoing research of her group focuses on the known existing clonally transmissible cancers arising in mammals. These are cancers that can be passed on between individuals by the transfer of living cancer cells that somehow manage to evade the immune system of their hosts.
Horizontal transfer of mitochondria is the movement of whole mitochondria and mitochondrial DNA between cells. Mitochondria from donor cells are transported and incorporated into the endogenous mitochondrial network of recipient cells contributing to changes in the bioenergetics profile and in other functional properties of recipient cells. Horizontal cell-to-cell transfer of mitochondria and mitochondrial genome can occur among mammalian cells in vitro and in vivo. Mitochondrial transfer supports the exogenous replacement of damaged mitochondria, thereby rescuing mitochondrial defects. Stem cells, immortalized cells or primary cells are usually used as mitochondrial donors in most studies. These cells may transfer mitochondria to surrounding cells in their niche, thus affecting cell differentiation, proliferation, tissue homeostasis, development and ageing.
Comparative oncology integrates the study of oncology in non-human animals into more general studies of cancer biology and therapy. The field encompasses naturally seen cancers in veterinary patients and the extremely low rates of cancers seen in large mammals such as elephants and whales.
Contagious reticulum cell sarcoma is a reticulum-cell sarcoma found in Syrian hamsters that can be transmitted from one hamster to another. It was first described in 1945.
A mastocytoma in dogs is a neoplasm (neoplasia) originating from mast cells in the domestic dog, which occurs mainly in the skin and subcutis. Mastocytoma are not only extremely common in dogs, but also tend to be much more malignant in them than in other animal species. The average survival time for malignant tumors is only four months, whereas for benign tumors it is over two years.