Cancer prevalence in dogs increases with age and certain breeds are more susceptible to specific kinds of cancers. Millions of dogs develop spontaneous tumors each year. Boxers, Boston Terriers and Golden Retrievers are among the breeds that most commonly develop mast cell tumors. Large and giant breeds, like Great Danes, Rottweilers, Greyhound and Saint Bernards, are much more likely to develop bone cancer than smaller breeds. Lymphoma occurs at increased rates in Bernese Mountain dogs, bulldogs, and boxers. It is important for the owner to be familiar with the diseases to which their specific breed of dog might have a breed predisposition.

The prevention of feline cancer mainly depends on the cat's diet and lifestyle, as well as an ability to detect early signs and symptoms of cancer prior to advancement to a further stage. If cancer is detected at an earlier stage, it has a higher chance of being treated, therefore lessening the chances of fatality. Taking domesticated cats for regular checkups to the veterinarian can help spot signs and symptoms of cancer early on and help maintain a healthy lifestyle. Further, due to advancements in research, prevention of certain types of feline illnesses remains possible. A widely known preventative of feline leukemia virus is the vaccine which was created in 1969. Subsequently, an immunofloures-cent antibody (IFA) test for the detection of FeLV in the blood of infected cats was formulated. The IFA test was mainly used to experiment the chances of felines being exposed to cancer. The results showed that 33% of cats who were exposed to FeLV related diseases were at a higher risk for acquiring it, while the cats that were left unexposed were left unaffected. FeLV is either spread through contagion or infection and once infected it is possible for cats to stay that way for the rest of their lives.

Interaction with other Cats

Interaction with other cats with strains or diseases related to FeLV can be a great risk factor for cats attaining FeLV themselves. Therefore, a main factor in prevention is keeping the affected cats in quarantine from the unaffected cats. Stray cats, or indoor/outdoor cats have been shown to be at a greater risk for acquiring FeLV, since they have a greater chance of interacting with other cats. Domesticated cats that are kept indoors are the least vulnerable to susceptible diseases.

Vaccines

Vaccines help the immune system fight off disease causing organisms, which is another key to prevention. However, vaccines can also cause tumors if not given properly. Vaccines should be given in the right rear leg to ease tumor removal process. Vaccines given in the neck or in between the shoulder blades are most likely to cause tumors and are difficult to remove, which can be fatal to cats. Reducing the number of vaccinations given to a cat may also decrease the risk for it developing a tumor.

Spaying and Neutering

Spaying and neutering holds many advantages to cats, including lowering the risk for developing cancer. Neutering male cats makes them less subjected to testicular cancer, FeLV, and FIV. Spaying female cats lowers the risk for mammary cancer, ovarian, or uterine cancer, as it prevents them from going into heat. Female cats should be spayed before their first heat, as each cycle of heat creates a greater risk for mammary cancer. Spaying a female cat requires the removal of the ovaries and uterus, which would eliminate their chances of developing cancer in these areas.

Exposure to Sun

The risk of skin cancer increases when a cat is exposed to direct sunlight for prolonged periods. White cats, or cats with white faces and ears, should not be allowed out on sunny days. Between the hours of 10:00 am to 4:00 pm, it is recommended to keep domesticated cats indoors, as the sun is at its highest peak between these times. Sun block is also available for cats, which can help prevent skin irritation, and a veterinarian should be contacted to find out which brands are appropriate and to use on cats.

Exposure to Secondhand Smoke

Cats living in a smoker’s household are three times more likely to develop lymphoma. Compared to living in a smoke-free environment, cats exposed to secondhand smoke also have a greater chance of developing squamous cell carcinoma or mouth cancer. Cancer is also developed mostly due to the cat's grooming habits. As cats lick themselves while they groom, they increase chances of taking in the toxic, cancer-causing carcinogens that gather on their fur, which are then exposed to their mucus membranes.

Lifestyle

Providing a cat with the healthiest lifestyle possible is the key to prevention. Decreasing the amount of toxins, including household cleaning products, providing fresh and whole foods, clean and purified water, and reducing the amount of indoor pollution can help cats live a longer and healthier life. To lessen susceptibility to diseases, domesticated cats should be kept inside the household for most of their lives to reduce the risk of interacting with other stray cats that could be infected with diseases.

Dogs can develop many of the same types of cancer as humans. Many canine cancers are described with the same terminology and use the same classification systems as human cancers.

- Mast cell tumors are the most common type of skin cancer in canines.

- Lymphoma

- Prostate cancer

- Brain cancer

Hemangiosarcoma is a type of cancer that develops almost exclusively in dogs, the only two other species known to have it are cats and horses. Hemangiosarcomas are tumors that form on the blood vessels, and can occur all over the body. These tumors can develop on the skin, subcutaneously, or on a blood vessel within an organ and are highly malignant. The tumors are most fatal when they rupture, causing the dog to suffer from severe loss of blood.

Dogs are one of three mammalian species that are known to suffer from a transmissible cancer. Canine transmissible venereal tumor (CTVT) is species specific and highly contagious. The cancerous cell lines are transmitted between individuals that are in close contact with each other through acts of intercourse, biting, scratching, or licking. The cancer is prevalent in populations of stray dogs or environments of uncontrolled copulation. The tumors occur around the area of external genitalia and can grow up to 15 cm in area. Canine transmissible venereal tumors can often be infected, ulcerated, and hemorrhagic.

Many types of skin tumors, both benign (noncancerous) and malignant (cancerous), exist. Approximately 20-40% of primary skin tumors are malignant in dogs and 50-65%

are malignant in cats. Not all forms of skin cancer in cats and dogs are caused by sun exposure, but it can happen occasionally. On dogs, the nose and pads of the feet contain sensitive skin and no fur to protect from the sun. Also, cats and dogs with thin or light-colored coats are at a higher risk of sun damage over their entire bodies.

Mast cell tumors mainly occur in older adult dogs, but have been known to occur on rare occasions in puppies. The following breeds are commonly affected by mast cell tumors:

- Boxer

- Staffordshire bull terrier

- Bulldog

- Basset hound

- Weimaraner

- Boston terrier

- Great Dane

- Golden retriever

- Labrador retriever

- Beagle

- German shorthaired pointer

- Scottish terrier

- Pug

- Shar pei

- Rhodesian ridgeback

Two types of mast cell tumors have been identified in cats, a mast cell type similar to dogs and a histiocytic type that appears as subcutaneous nodules and may resolve spontaneously. Young Siamese cats are at an increased risk for the histiocytic type, although the mast cell type is the most common in all cats and is considered to be benign when confined to the skin.

Mast cell tumors of the skin are usually located on the head or trunk. Gastrointestinal and splenic involvement is more common in cats than in dogs; 50 percent of cases in dogs primarily involved the spleen or intestines. Gastrointestinal mast cell tumors are most commonly found in the muscularis layer of the small intestine, but can also be found in the large intestine. It is the third most common intestinal tumor in cats, after lymphoma and adenocarcinoma.

Diagnosis and treatment are similar to that of the dog. Cases involving difficult to remove or multiple tumors have responded well to strontium-90 radiotherapy as an alternative to surgery. The prognosis for solitary skin tumors is good, but guarded for tumors in other organs. Histological grading of tumors has little bearing on prognosis.

Laboratory cats have been used in research for a wide range of diseases including stroke and diabetes to AIDS. Less than 1% of research on animal illnesses have been dedicated to cats.

Despite opposition from organizations such as those advocating animal rights, controversial animal testing is still used in cancer research centers. These research practices are continually being conducted on the basis that its benefits to humans outweigh the costs to humans, despite the unfair costs to innocent non-human animals. In some US states, animal testing laboratories get some of their feline test subjects from animal shelters.

According to Kim Sterling, associate teaching professor of oncology at the University of Missouri College of Veterinary Medicine, the use of small animals in predicting human health care procedures is of significant benefit to humans because they are affected in similar, but not exactly the same, ways by the same diseases. This is the same analogy used in reference to cats and their unwilling role in advancing human cancer treatment research.

It is research like this that has led to a potential link between cat parasites and brain cancer in humans. Cats carry the parasite toxoplasma gondii. According to research ecologist Kevin Lafferty, of the University of California, Santa Barbara, this parasite is known to “behave in ways that could stimulate cells towards cancerous states”.

Therefore, research on cats with this parasite can help to better understand the risks of brain cancer for humans in contact with such cats.

Cats have also been used to further studies in the field of Cancer stem cell research. Small animals, like cats, experience faster rates of cancer development. As a result, they are good preclinical models for understanding processes like immortalization and its role in promoting cancerous tumors. The absence of immortalization means a cell can no longer undergo malignant transformation. Since these transformations are the basis for cancerous cell reproduction, this research can prove useful for future cancer treatments and understanding how to stop the spread of cancer in the body.

However, feline cancer research is not limited to what laboratory cats can do for other animals, there is also research being done by humans to see what can be done to improve treatment options for feline cancer. Advances, though slower than that in other animals, are being made in the field of feline cancer. This includes advances in chemotherapy research, immunization protocols and radiation therapy. In addition, there are clinical trials offering trial research treatment options for cats with cancer.

One of such treatments is the cat's claw. Although they share the same name, the cat’s claw (also known as "Uncaria tomentosa" or uña de gato) refers not to the animal cat but to a native plant of the Amazon Rainforest in Peru, South America. Cat's claw is still under research for its immunotherapic, antiproliferative abilities in suppressing cancer proliferation in humans; however, it has been deemed suitable for cat cancer treatment.

Nonetheless, feline cancer research into this, as well as other treatment options, remains an ongoing process.

Mammary tumors are the third most common neoplasia in cats, following lymphoid and skin cancers. The incidence of mammary tumors in cats is reduced by 91 percent in cats spayed prior to six months of age and by 86 percent in cats spayed prior to one year, according to one study. Siamese cats and Japanese breeds seem to have increased risk, and obesity also appears to be a factor in tumor development. Malignant tumors make up 80 to 96 percent of mammary tumors in cats, almost all adenocarcinomas. Male cats may also develop mammary adenocarcinoma, albeit rarely, and the clinical course is similar to female cats. As in dogs, tumor size is an important prognostic factor, although for tumors less than three centimeters the individual size is less predictive. According to one study, cats with tumors less than three cm had an average survival time of 21 months, and cats with tumors greater than three cm had an average survival of 12 months. About 10 percent of cat mammary tumors have estrogen receptors, so spaying at the time of surgery has little effect on recurrence or survival time. Metastasis tends to be to the lungs and lymph nodes, and rarely to bone. Diagnosis and treatment is similar to the dog. There is a better prognosis with bilateral radical surgery (removing the both mammary chains) than with more conservative surgery. Doxorubicin has shown some promise in treatment.

Most mammary tumors in rats are benign fibroadenomas, which are also the most common tumor in the rat. Less than 10 percent are adenocarcinomas. They occur in male and female rats. The tumors can be large and occur anywhere on the trunk. There is a good prognosis with surgery. Spayed rats have a decreased risk of developing mammary tumors.

The specific treatment will depend on the tumor's type, location, size, and whether the cancer has spread to other organs. Surgical removal of the tumor remains the standard treatment of choice, but additional forms of therapy such as radiation therapy, chemotherapy, or immunotherapy exist.

When detected early, skin cancer in cats and dogs can often be treated successfully. In many cases, a biopsy can remove the whole tumor, as long as the healthy tissues removed from just outside the tumor area do not contain any cancer cells.

New vaccine protocols have been put forth by the American Association of Feline Practitioners that limit type and frequency of vaccinations given to cats. Specifically, the vaccine for feline leukemia virus should only be given to kittens and high risk cats. Feline rhinotracheitis/panleukopenia/calicivirus vaccines should be given as kittens, a year later and then every three years. Also, vaccines should be given in areas making removal of VAS easier, namely: as close as possible to the tip of the right rear paw for rabies, the tip of the left rear paw for feline leukemia (unless combined with rabies), and on the right shoulder—being careful to avoid the midline or interscapular space—for other vaccines (such as FVRCP). There have been no specific associations between development of VAS and vaccine brand or manufacturer, concurrent infections, history of trauma, or environment.

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.

The term "angiosarcoma", when used without a modifier, usually refers to hemangiosarcoma. However, glomangiosarcoma (8710/3) and lymphangiosarcoma (9170/3) are distinct conditions [in humans]. Hemangiosarcomas are commonly associated with toxic exposure to thorium dioxide (Thorotrast), vinyl chloride, and arsenic.

Inflammation in the subcutis following vaccination is considered to be a risk factor in the development of VAS, and vaccines containing aluminum were found to produce more inflammation. Furthermore, particles of aluminum adjuvant have been discovered in tumor macrophages. In addition, individual genetic characteristics can also contribute to these injection-site sarcomas. The incidence of VAS is between 1 in 1,000 to 1 in 10,000 vaccinated cats and has been found to be dose-dependent. The time from vaccination to tumor formation varies from three months to eleven years. Fibrosarcoma is the most common VAS; other types include rhabdomyosarcoma, myxosarcoma, chondrosarcoma, malignant fibrous histiocytoma, and undifferentiated sarcoma.

Similar examples of sarcomas developing secondary to inflammation include tumors associated with metallic implants and foreign body material in humans, and sarcomas of the esophagus associated with "Spirocerca lupi" infection in dogs and ocular sarcomas in cats following trauma. Cats may be the predominant species to develop VAS because they have an increased susceptibility to oxidative injury, as evidenced also by an increased risk of Heinz body anemia and acetaminophen toxicity.

Compared to other breeds of dog, Scottish terriers have a much increased risk of developing transitional cell carcinoma.

Prognosis is separated into three groups.

- Stage I osteosarcoma is rare and includes parosteal osteosarcoma or low-grade central osteosarcoma. It has an excellent prognosis (>90%) with wide resection.

- Stage II prognosis depends on the site of the tumor (proximal tibia, femur, pelvis, etc.), size of the tumor mass, and the degree of necrosis from neoadjuvant chemotherapy. Other pathological factors such as the degree of p-glycoprotein, whether the tumor is cxcr4-positive, or Her2-positive are also important, as these are associated with distant metastases to the lung. The prognosis for patients with metastatic osteosarcoma improves with longer times to metastases, (more than 12 months to 4 months), a smaller number of metastases, and their resectability. It is better to have fewer metastases than longer time to metastases. Those with a longer length of time (more than 24 months) and few nodules (two or fewer) have the best prognosis, with a two-year survival after the metastases of 50%, five-year of 40%, and 10-year of 20%. If metastases are both local and regional, the prognosis is worse.

- Initial presentation of stage III osteosarcoma with lung metastases depends on the resectability of the primary tumor and lung nodules, degree of necrosis of the primary tumor, and maybe the number of metastases. Overall survival prognosis is about 30%.

Deaths due to malignant neoplasms of the bones and joints account for an unknown number of childhood cancer deaths. Mortality rates due to osteosarcoma have been declining at about 1.3% per year. Long-term survival probabilities for osteosarcoma have improved dramatically during the late 20th century and approximated 68% in 2009.

Several research groups are investigating cancer stem cells and their potential to cause tumors along with genes and proteins causative in different phenotypes.Radiotherapy for unrelated conditions may be a rare cause.

- Familial cases where the deletion of chromosome 13q14 inactivates the retinoblastoma gene is associated with a high risk of osteosarcoma development.

- Bone dysplasias, including Paget's disease of bone, fibrous dysplasia, enchondromatosis, and hereditary multiple exostoses, increase the risk of osteosarcoma.

- Li–Fraumeni syndrome (germline TP53 mutation) is a predisposing factor for osteosarcoma development.

- Rothmund–Thomson syndrome (i.e. autosomal recessive association of congenital bone defects, hair and skin dysplasias, hypogonadism, and cataracts) is associated with increased risk of this disease.

- Large doses of Sr-90 emission from nuclear reactor, nicknamed bone seeker increases the risk of bone cancer and leukemia in animals, and is presumed to do so in people.

Despite persistent rumors suggesting otherwise, there is no clear association between water fluoridation and cancer or deaths due to cancer, both for cancer in general and also specifically for bone cancer and osteosarcoma. Series of research concluded that concentration of fluoride in water doesn't associate with osteosarcoma. The beliefs regarding association of fluoride exposure and osteosarcoma stem from a study of US National Toxicology program in 1990, which showed uncertain evidence of association of fluoride and osteosarcoma in male rats. But there is still no solid evidence of cancer-causing tendency of fluoride in mice. Fluoridation of water has been practiced around the world to improve citizens' dental health. It is also deemed as major health success. Fluoride concentration levels in water supplies are regulated, such as United States Environmental Protection Agency regulates fluoride levels to not be greater than 4 milligrams per liter. Actually, water supplies already have natural occurring fluoride, but many communities chose to add more fluoride to the point that it can reduce tooth decay. Fluoride is also known for its ability to cause new bone formation. Yet, further research shows no osteosarcoma risks from fluoridated water in humans. Most of the research involved counting number of osteosarcoma patients cases in particular areas which has difference concentrations of fluoride in drinking water. The statistic analysis of the data shows no significant difference in occurrences of osteosarcoma cases in different fluoridated regions. Another important research involved collecting bone samples from osteosarcoma patients to measure fluoride concentration and compare them to bone samples of newly diagnosed malignant bone tumors. The result is that the median fluoride concentrations in bone samples of osteosarcoma patients and tumor controls are not significantly different. Not only fluoride concentration in bones, Fluoride exposures of osteosarcoma patients are also proven to be not significantly different from healthy people.

Fibrosarcoma occurs most frequently in the mouth in dogs . The tumor is locally invasive, and often recurs following surgery . Radiation therapy and chemotherapy are also used in treatment. Fibrosarcoma is also a rare bone tumor in dogs.

In cats, fibrosarcoma occurs on the skin. It is also the most common vaccine-associated sarcoma. In 2014, Merial launched Oncept IL-2 in Europe for the management of such feline fibrosarcomas.

Treatment includes chemotherapy and, where practical, removal of the tumor with the affected organ, such as with a splenectomy. Splenectomy alone gives an average survival time of 1–3 months. The addition of chemotherapy, primarily comprising the drug doxorubicin, alone or in combination with other drugs, can increase the average survival time to 2-4 months, or more.

A more favorable outcome has been demonstrated in recent research conducted at University of Pennsylvania Veterinary School, in dogs treated with a compound derived from the Coriolus versicolor (commonly known as "Turkey Tail") mushroom:

“We were shocked,” Cimino Brown said. “Prior to this, the longest reported median survival time of dogs with hemangiosarcoma of the spleen that underwent no further treatment was 86 days. We had dogs that lived beyond a year with nothing other than this mushroom as treatment.”There were not statistically significant differences in survival between the three dosage groups, though the longest survival time was highest in the 100 mg group, at 199 days, eclipsing the previously reported survival time.

The results were so surprising, in fact, that the researchers asked Penn Vet pathologists to recheck the dogs’ tissue biopsies to make sure that the dogs really had the disease.

“They reread the samples and said, yes, it’s really hemangiosarcoma,” Cimino Brown said.

Chemotherapy is available for treating hemangiosarcoma, but many owners opt not to pursue that treatment once their dog is diagnosed.

“It doesn’t hugely increase survival, it’s expensive and it means a lot of back and forth to the vet for the dog,” Cimino Brown said. “So you have to figure in quality of life.”

This treatment does not always work. So, one should always be prepared for their pet to have the same survival time as a dog who is untreated.

Visceral hemangiosarcoma is usually fatal even with treatment, and usually within weeks or, at best, months. In the skin, it can be cured in most cases with complete surgical removal as long as there is not visceral involvement.

Bladder cancer in cats and dogs usually is transitional cell carcinoma, which arises from the epithelial cells that line the bladder. Less often, cancer of the urinary bladder is squamous cell carcinoma, adenocarcinoma, or rhabdomyosarcoma.

Depending on the pet's unique condition, there are several treatment options, including surgery, chemotherapy and radiation therapy. Treating the pain adequately is also of crucial importance to improve the pet's quality of life, especially if amputation is not performed.

Tumors that develop within the liver may be either benign (noncancerous) or malignant (cancerous). Tumors can start in the liver, or spread to the liver from another cancer in the body. Malignant liver tumors have been reported to metastasize to other organs such as regional lymph nodes, lungs, kidneys, pancreas, spleen and others.

In infants, fibrosarcoma (often termed congenital infantile fibrosarcoma) is usually congenital. Infants presenting with this fibrosarcoma usually do so in the first two years of their life. Cytogenetically, congenital infantile fibrosarcoma is characterized by the majority of cases having a translocation between chromosomes 12 and 15 (notated as t(12;15)(p13;q25)) that results in formation of the fusion gene, "ETV6-NTRK3", plus individual cases exhibiting trisomy for chromosomes 8, 11, 17, or 20. The histology, association with the "ETV6-NRTK3" fusion gene as well as certain chromosome trisomies, and the distribution of markers for cell type (i.e. cyclin D1 and Beta-catenin) within this tumor are similar to those found in the cellular form of mesoblastic nephroma. Indeed, mesoblastic nephroma and congenital infantile sarcoma appear to be the same disease with the exception that mesoblastic lymphoma originates in the kidney whereas congenital infantile sarcoma originates in non-renal tissues.

A perianal gland tumor is a type of tumor found near the anus in dogs that arises from specialized glandular tissue found in the perineum. Perianal glands do not exist in cats. It is also known as a hepatoid tumor because of the similarity in cell shape to hepatocytes (liver cells). It is most commonly seen in intact (not neutered) dogs and is the third most common tumor type in intact male dogs. There are two types of perianal gland tumors, perianal gland adenomas, which are benign, and perianal gland adenocarcinomas, which are malignant. Both have receptors for testosterone. Perianal gland adenomas are three times more likely to be found in intact male dogs than females, and perianal gland adenocarcinomas are ten times more common in male dogs than females. The most commonly affected breeds for adenomas are the Siberian Husky, Cocker Spaniel, Pekingese, and Samoyed; for adenocarcinomas the most commonly affected breeds are the Siberian Husky, Bulldog, and Alaskan Malamute.

Perianal gland tumors are located most commonly in the skin around the anus, but can also be found on the tail or groin. Adenomas are more common, making up 91 percent of perianal gland tumors in one study. Adenomas and adenocarcinomas look alike, both being round, pink and usually less than three centimeters in width. Adenocarcinomas are more likely to be multiple and invasive into the underlying tissue, and they can metastasize to the lymph nodes, liver, and lungs.

Both types should be removed and sent to a pathologist for identification. However, 95 percent of perianal gland adenomas will disappear after neutering the dog. Removing the tumor and neutering the dog at the same time will help prevent recurrence. Dogs with perianal gland adenocarcinomas should be treated with aggressive surgery and the radiation therapy and chemotherapy if necessary.

The most common bone tumor is called osteosarcoma, and typically affects middle-age to older dogs of large and giant breeds. Osteosarcoma is less common in cats. Osteosarcoma is an aggressive cancer that can develop in any bone of the body but the majority is seen in the limbs (e.g. long bones such as radius, humerus, femur, and tibia).

The average age at which intestinal tumors are diagnosed ranges between 10–12 years for cats and 6 to 9 years for dogs. There are many different types of intestinal tumors, including lymphoma, adenocarcinoma, mast cell tumor, and leiomyosarcoma.