Introduction to Cancer in Cats
Cats are susceptible to a variety of cancers. Among the most common are lymphoma, squamous cell carcinoma (skin cancer), mammary cancer, mast cell tumors, oral tumors, fibrosarcoma (soft tissue cancer) , osteosarcoma (bone cancer), respiratory carcinoma, intestinal adenocarcinoma, and pancreatic/liver adenocarcinoma. The disease has become so prevalent that it is now the most common cause of death in cats.(1)
Certain breeds are more prone to certain cancers than others. Signs and symptoms differ depending on the type and stage of the cancer. Detection and diagnosis requires some detective work. Tumors that are visible and/or detectable by touch are most easily identified. Vets often perform additional tests to make an accurate diagnosis. Along with a physical exam, they may perform blood and urine tests, cytology, imaging and biopsies.
Treatment options vary and include surgery, chemotherapy, radiation, immunotherapy, photodynamic therapy, or a combination of these. In many cases, cancer can be successfully treated. Early detection and diagnosis is critical. Regular visits to the veterinarian can help prevent and manage cancer. The American Veterinary Medical Association recommends twice-a-year wellness exams for all cats.(2) Because the causes of cancer in cats are similar to those in humans, risk can be reduced by lowering the animal's exposure to harmful carcinogens, including tobacco smoke.(3)
Feline Leukemia and the Feline Leukemia Virus
Overview and Transmission
In humans, some viruses can lead to cancer. An example is human papilloma virus (HPV) which is the causative agent of most cases of cervical cancer. Viral infection can also lead to cancer in animals. Feline leukemia (FeLV; informally known as "Fee-Leuk") is an RNA virus (a retrovirus) that infects less than 2% of healthy, domestic cats in the U.S.(1) (2) Infection is more prevalent in high-risk populations (i.e. cats with outdoor access and/or frequent social interactions).(1)
The virus is spread from one cat to another via saliva, nasal secretions, feces, and milk.(3) (4) It is transmitted during various forms of contact, from friendly grooming to not-so-friendly biting. The virus can also be passed to a developing kitten during pregnancy. The age and time of infection affect the progression and clinical outcome of the virus. Kittens are more likely to be infected and more likely to develop more severe complications.(5) In most cases, FeLV initially infects lymphocytes in the back of the throat (oropharynx), which travel to the bone marrow, where virally infected cells are produced very rapidly.(6)
In most environments, the Feline leukemia virus cannot survive for long outside of the host. It can be "killed" with soap and disinfectants. At this time, studies show no evidence that FeLV can be transmitted from infected cats to humans.(7) However, because FeLV positive cats may carry other diseases, infants, elderly individuals, and immunosuppressed individuals may want to avoid contact.
Symptoms
Infected animals may develop anemia, lymphoma, and other conditions. The FeLV-C subtype binds to and impedes the function of a heme transport protein on the surface of developing red blood cells. The result is a decrease in red blood cell numbers (anemia).(8) (9) Signs of anemia in cats include paleness of the skin, tongue, gums, and mucous membranes surrounding the eye. FeLV- induced lymphomas are some of the most frequent tumors seen in cats. Symptoms depend on the location of the tumor, and may include weight loss, rough hair coat, loss of appetite, vomiting, diarrhea, respiratory distress, swelling of the lymph nodes and more. FeLV is also linked to diseases of the kidneys, joints, lymph nodes, small intestine, liver and nervous system. Depression of the immune system makes infected cats more susceptible to infections. As a result, they may be infected by organisms that healthy cats usually fend off. It is possible for FeLV positive cats to remain healthy. However, the prognosis is poor for cats with persistent active infection.(6)
Detection of FeLV
Veterinarians use several different laboratory tests to detect FeLV. These include 1) an antigen enzyme-linked immunosorbent assay (ELISA) and 2) an indirect immunofluorescent antibody assay (IFA). Both tests use blood samples to detect the presence of a protein that indicates FeLV infection. This protein is called p27, and is part of the structure of the virus.(6) Inconclusive results may require additional testing with other methods, such as a specific type of polymerase chain reaction (PCR), which can detect FeLV DNA in infected animals.
Treatment for FeLV Infection
Currently there is no cure for FeLV. However there are a number of things that pet owners can do to manage FeLV positive cats, as recommended by veterinarians and experts:
- Visit the vet every 6 months for a physical examination, complete blood count, urine analysis, and other tests
- Carefully monitor the cat's health (i.e. measure and record weight loss)
- Provide cat(s) with a healthy and balanced diet. Avoid uncooked meat and eggs, as well as unpasteurized dairy products to prevent food-borne infections
- Confine cats to indoor environments to reduce exposure to harmful organisms
Antiviral therapy has been used in FeLV positive cats, but the effectiveness of the drugs is limited and they can be toxic. Medications to control and restore the immune system (immunomodulators) are also used. However data to support the proposed health benefits of these agents are limited.(5) (7)
Prevention of FeLV Infection
Infection with FeLV can be prevented by vaccination. The vaccine is classified as non-core, which means it can be considered optional. However both the American Association of Feline Practitioners (AAFP) and the European Advisory Board on Cat Disease (ABCD) recommend that all cats with uncertain FeLV status and/or are at risk of exposure be vaccinated. Kittens are often vaccinated at 8-9 weeks of age and again at 12 weeks of age. Research shows that the vaccine will confer immunity for up to 1 year. Many vets recommend a booster vaccination 1 year after initial vaccination and annually thereafter. Because cats become less susceptible with age, some vets consider vaccination every 2-3 years sufficient for older animals.(6)
Feline Squamous Cell Carcinoma
Introduction
Squamous Cell Carcinoma (SCC) is a cancer that occurs in cats and dogs. The tumors can appear many places but are seen most commonly on and around the eyes, ears, nose, mouth, and areas with little hair.
Squamous Cell Carcinoma (SCC) is a cancer that occurs in cats and dogs. The tumors can appear many places but are seen most commonly on and around the eyes, ears, nose, mouth, and areas with little hair.
Risk Factors/Detection/Staging
The primary cause of SCC is sunlight over-exposure, which is especially harmful to fair-haired cats. Age and exposure to cigarette smoke also increase the risk for SCC.(1) At first, SCC tumors look much like other common skin irritations, making them difficult to identify. Scabs, hair loss, irritated skin, loss of teeth with limited healing, and raised red bumps on the skin are all possible sign of SCC.(1) Crusty sores can appear and develop into deep ulcers that bleed when irritated. In later stages, the cancer may spread to the lymph nodes and lungs. Staging of the cancer may involve chest X-rays and testing lymph fluid.(2) In advanced cases, SCC tumors can cause tissue death and destroy bone structure, leading to pain, discomfort, and possibly death.
The primary cause of SCC is sunlight over-exposure, which is especially harmful to fair-haired cats. Age and exposure to cigarette smoke also increase the risk for SCC.(1) At first, SCC tumors look much like other common skin irritations, making them difficult to identify. Scabs, hair loss, irritated skin, loss of teeth with limited healing, and raised red bumps on the skin are all possible sign of SCC.(1) Crusty sores can appear and develop into deep ulcers that bleed when irritated. In later stages, the cancer may spread to the lymph nodes and lungs. Staging of the cancer may involve chest X-rays and testing lymph fluid.(2) In advanced cases, SCC tumors can cause tissue death and destroy bone structure, leading to pain, discomfort, and possibly death.
Treatment
Several treatment options exist for SCC and they may be combined to increase success. As with other cancers, the earlier SCC is detected, the more likely the treatment will be successful. Tumors in the lower jaw or upper ear can be surgically removed. Vets attempt to preserve as much healthy tissue as possible. For tumors in the lower jaw, vets can perform a surgical Mandibulectomy, in which they attempt to remove the cancerous area(s). The amount of the jaw tissue and bone removed depends on the tumor. Possible side effects include difficulty eating and grooming, drooling, and poor appetite.(1) Despite a cancer reoccurrence rate of 38% and post-operation complications, one survey revealed that over 80% of owners whose cats had surgery would choose this treatment again.(1)
Chemotherapy alone has not proven effective, but there is evidence that it may be effective when combined with other treatments. A combination of the chemotherapy agent mitoXANTRONE with external beam radiation therapy gave better results than either treatment option used alone.(3) If the tumor is in the mouth, radiation should be considered with caution as it can cause severe inflammation. Side effects may prevent normal eating and require the use of a feeding tube.
Several treatment options exist for SCC and they may be combined to increase success. As with other cancers, the earlier SCC is detected, the more likely the treatment will be successful. Tumors in the lower jaw or upper ear can be surgically removed. Vets attempt to preserve as much healthy tissue as possible. For tumors in the lower jaw, vets can perform a surgical Mandibulectomy, in which they attempt to remove the cancerous area(s). The amount of the jaw tissue and bone removed depends on the tumor. Possible side effects include difficulty eating and grooming, drooling, and poor appetite.(1) Despite a cancer reoccurrence rate of 38% and post-operation complications, one survey revealed that over 80% of owners whose cats had surgery would choose this treatment again.(1)
Chemotherapy alone has not proven effective, but there is evidence that it may be effective when combined with other treatments. A combination of the chemotherapy agent mitoXANTRONE with external beam radiation therapy gave better results than either treatment option used alone.(3) If the tumor is in the mouth, radiation should be considered with caution as it can cause severe inflammation. Side effects may prevent normal eating and require the use of a feeding tube.
Cryotherapy or freeze-surgery involves insertion of a probe that freezes the tumor, killing the cancer cells. Cryotherapy is an option for tumors under 1 cm (about 0.4 inch) in diameter. The rate of reoccurrence is high for larger tumors.(4) Cryotherapy is a good option for tumors on the upper ear because the position allows for direct and aggressive treatment.
Photodynamic therapy (PT) is a newer treatment option for Squamous Cell Carcinoma, and is not available everywhere. This type of treatment involves putting a light-sensitive material in the tumor and exposing the tumor to a specific wavelength of light. This causes the light-sensitive chemical to become active and destroy the tumor cells.(5) It can be used repeatedly and with other treatment options.(6) The side effects include swelling, redness, sensitivity to light, and death of healthy tissue around the tumor site. A recent study followed 12 cats with SCC that were treated with PT. Researchers found that when used alone, PT resulted in shrinkage of shallow tumors of the nose and ear, but had little effect on deeper tumors. When used in combination with surgery, two cats exhibited a partial response to therapy, and one exhibited a complete response.(5)
Feline Mammary Cancer
Introduction
Feline mammary cancer (FMC) is the third most common cancer in female cats. It is very uncommon in males, but cases have been reported.(1) The mammary gland tumors that result from FMC can be benign or malignant. However, research shows that 80-96% of mammary tumors are malignant, meaning that they can invade nearby tissues, and are capable of metastasis (spreading to distant parts of the body).(1) (2) Unfortunately malignant mammary tumors tend to be much more harmful.
Feline mammary cancer (FMC) is the third most common cancer in female cats. It is very uncommon in males, but cases have been reported.(1) The mammary gland tumors that result from FMC can be benign or malignant. However, research shows that 80-96% of mammary tumors are malignant, meaning that they can invade nearby tissues, and are capable of metastasis (spreading to distant parts of the body).(1) (2) Unfortunately malignant mammary tumors tend to be much more harmful.
Cats have four mammary glands on each side of their body, any of which can be affected by FMC. They are referred to as axillary, thoracic, abdominal, and inguinal glands. These glands are the sites of primary tumor growth. As with breast cancer in women, FMC is highly metastatic. As a result, this type of cancer can spread to the lungs, the lining of the lungs and chest cavity (pleura), liver, regional lymph nodes, and other parts of the body.
Genes that have been targeted in human breast cancer research have also been studied in feline mammary cancer. HER-2/neu is the gene that encodes the human epidermal growth factor receptor (type 2) protein. This protein resides on cell surfaces, where it can interact with growth signals. If gene amplification creates extra copies of the HER-2 gene, then its corresponding protein will also be overexpressed. This is thought to lead to increased cell proliferation. HER-2 overexpression has been detected in up to 30% of human breast cancer cases.(1) Similarly, it occurs in 30% of feline mammary cancer cases.(3)
Risk Factors/Detection/Staging
While all feline breeds may be affected by FMC, some are at a higher risk than others.(3) Studies have shown the Siamese breed to have twice the risk of developing this type of cancer.(1) (4) Risk increases with age up to 14 years, with an average age of tumor development between 10 and 11 years.(1) (2) Early spaying reduces risk. According to one study, intact females are 7 times more likely to develop mammary tumors than cats that are spayed at a young age.(5) The latest age at which spaying effectively reduces FMC risk has not been determined.
While all feline breeds may be affected by FMC, some are at a higher risk than others.(3) Studies have shown the Siamese breed to have twice the risk of developing this type of cancer.(1) (4) Risk increases with age up to 14 years, with an average age of tumor development between 10 and 11 years.(1) (2) Early spaying reduces risk. According to one study, intact females are 7 times more likely to develop mammary tumors than cats that are spayed at a young age.(5) The latest age at which spaying effectively reduces FMC risk has not been determined.
FMC is most often detected when pet owners or veterinarians feel a mass during examination of the mammary region. However masses can also indicate other conditions, such as severely inflamed lesions, cysts, follicular tumors, and others.(3) Histology can be used to confirm the diagnosis and classify the lesion. Tumors are graded as well differentiated, moderately differentiated, or poorly differentiated, based on the appearance of the tissue/cells under a microscope.
Veterinarians and researchers agree that tumor size is the most important prognostic factor in FMC cases, affecting the progression of the disease and the survival time.(3) In general, larger tumors have a worse prognosis. Lymph node involvement and degree of metastasis also determine the severity of FMC cases.
Treatment
Surgical removal of mammary tumors is the most common treatment choice. This may include nodulectomy (removal of one or more cell clusters), partial or complete removal of the affected mammary gland(s), removal of lymph nodes, and mastectomy (removal of all glands on the affected side(s)). Veterinarians may use radiation or chemotherapy in addition to surgery. Drugs used to treat FMC include 5-fluoroucil, doxorubicin, cyclophosphamide, methotrexate, prednisone, and vincristine.(6) It has been shown that cats that respond to doxorubicin-cyclophosphamide treatments survive for longer periods of time.(6)
Surgical removal of mammary tumors is the most common treatment choice. This may include nodulectomy (removal of one or more cell clusters), partial or complete removal of the affected mammary gland(s), removal of lymph nodes, and mastectomy (removal of all glands on the affected side(s)). Veterinarians may use radiation or chemotherapy in addition to surgery. Drugs used to treat FMC include 5-fluoroucil, doxorubicin, cyclophosphamide, methotrexate, prednisone, and vincristine.(6) It has been shown that cats that respond to doxorubicin-cyclophosphamide treatments survive for longer periods of time.(6)
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