Cancer in Cats

Acute leukemia is a systemic cancer characterized by the infiltration of immature lymphocytes or myelocytes (two types of white blood cells) called in the bone marrow (and commonly in the liver and spleen as well). Patients with acute leukemia are typically quite ill due to their disease. Affected animals are typically young (less than 5 years of age). There is a male gender predilection in some studies.

What causes this type of cancer in dogs and cats?
  • The feline leukemia virus (FeLV) was a common cause of leukemias in the past. With the current practice of testing cats for both the FeLV and FIV viruses, the occurrence of FeLV positive cats has dramatically declined. Most cases of acute lymphocytic and myeloid leukemia are not inherited.
What are the common signs of this cancer?
  • Patients will have variable degrees of anemia (low red cell count), thrombocytopenia (low platelet count), and neutropenia (low neutrophil count-a type of white blood cell)
  • Clinical signs in patients with acute leukemia are usually severe due to the level of bone marrow suppression
  • Affected cats typically have a history of weight loss, excessive drinking and urination, loss of  appetite, and lethargy
  • Findings on physical examination can include signs of hemorrhage (bleeding), enlargement of the spleen and liver, and lymph node enlargement
How is it diagnosed?
  • CBC (with pathology review)/chemistry panel/urinalysis/FeLV/FIV tests
  • 3 view thoracic radiographs
  • Abdominal ultrasound
  • Bone marrow aspirate/evaluation
  • Immunophenotyping via flow cytometry—a test that allows veterinarians to evaluate the exact type of white blood cells that are in the blood or bone marrow. This test may be beneficial in distinguishing acute myelogenous leukemia from acute lymphoblastic leukemia from stage V lymphoma, although sometimes telling the difference between these conditions can be very difficult.
How is this cancer treated?
  • Patients with acute leukemia require aggressive therapy
  • Aggressive chemotherapy with a multi-agent IV chemotherapy protocol is the treatment of choice
  • The specific chemotherapy protocol will be based on the results of the immunophenotype (which tells us the type of white blood cell).
  • Patients may also require intense supportive therapy with treatments such as blood transfusions, broad spectrum antibiotic therapy, IV fluid therapy,  and nutritional support
  • In-depth monitoring is also required to monitor for signs of infection, signs of bleeding, and signs of abnormal clot formation or DIC (disseminated intravascular coagulation)
What is the prognosis for dogs and cats with this cancer?
  • Prognosis of acute leukemia is typically poorer than with lymphoma
  • Survival times for those cats that respond to treatment are around 6 months with some cats living many more months
  • If the patient does not respond to therapy, survival time is usually weeks as infection and bleeding problems are very common with this disease.
What is on the horizon for this cancer?
  • Bone marrow transplantation is currently the state-of-the-art for the treatment of this disease in people and veterinary oncologists are actively trying to adapt it for cats.

Lymphoma accounts for one-third of all malignancies in cats and occurs in various primary anatomic sites, such as the gastrointestinal tract, kidneys, mediastinum (chest cavity) and spleen. Unlike in dogs with lymphoma, cats generally do not present with generalized peripheral lymph node enlargement.The occurrence of feline lymphoma has been strongly associated with infection by the feline leukemia virus (FeLV) and certain strains of the feline immunodeficiency virus (FIV) although over the last 10 years, the use of testing and vaccination has dramatically reduced the incidence of FeLV infection in the United States. A combination of 5 chemotherapy drugs is reported to be the most effective method to treat most types of lymphoma in cats. Radiation therapy and surgery, along with chemotherapy, are used to treat the more localized forms of lymphoma (such as intra-nasal or ocular.)Treatment goals are to improve quality of life by achieving remission with minimal toxicity and side effects from the drugs.

What causes this type of cancer in dogs and cats?
  • The FeLV virus has been shown to cause lymphoma and the FIV virus can predispose infected animals to develop lymphoma. Second hand smoke is also known to cause gastrointestinal lymphoma in cats--the carcinogens from the smoke are thought to settle on cat's fur, and when the cat grooms itself, get ingested.
  • Lymphoma is not contagious to other cats or humans. However, if the patient is FeLV positive, other cats in the household should be tested for this viral infection.
What are the common signs of this cancer?
  • The signs of lymphoma are often correlated with the area of involvement --the gastrointestinal tract, the mediastinum, the lymphatic organs (lymph nodes, liver, spleen and/or bone marrow), kidneys, the eye (ocular form), the central nervous system, the nasal cavity, the skin and other areas.
  • Signs can include weight loss, vomiting, anorexia  (loss of appetite), lethargy (loss of energy level), diarrhea, excessive thirst, or a mass that is felt in the abdomen
How is it diagnosed?
  • The most common methods used to diagnose lymphoma include fine needle aspiration, cutting needle biopsy or endoscopic biopsy.
  • Occasionally a blood test may reveal circulating cancerous lymphocytes.
  • Depending upon the site of the lymphoma, the appropriate diagnostic method may require general anesthesia.
  • Often blood tests, radiographic studies, and sometimes bone marrow aspiration are needed to stage the lymphoma, to determine the extent of the cancer.
  • The diagnostic work-up should include a complete blood count, platelet count, biochemistry profile and urinalysis.
  • These tests also help to identify the existence of other unrelated illnesses (such as kidney disease) which may interfere with our ability to safely administer chemotherapy. Thoracic and abdominal radiographs, abdominal ultrasound and CT scan or MRI tests may be needed to determine the extent of the tumor. If the liver, spleen or kidneys are enlarged, ultrasound-guided fine needle aspiration is recommended to determine if these organs are infiltrated with lymphoma cells.
  • A blood test for FeLV and feline immunodeficiency virus (FIV) is recommended to establish a prognosis for survival time and possible virus-associated complicating illnesses.
How is this cancer treated?
  • Because lymphoma is a systemic disease, chemotherapy is the preferred treatment modality. In selected cases, prior to the administration of chemotherapy, radiation therapy or surgery may be used to treat lymphoma localized to a defined site.
  • It is important to understand that lymphoma is not curable. 
  • Therapeutic success consists of achieving prolonged remission  (control) of the lymphoma and associated clinical signs. We strive to avoid toxicity or side effects from chemotherapy that interfere with the patient's quality of      life.  The duration of remission is  extremely variable, depending on tumor location, extent of tumor within one or several sites and presence of other mitigating circumstances (ie anemia, kidney disease). 
  • The chemotherapy drugs used to treat this cancer  are a combination of oral and injectable medications administered at specific time intervals.  This is  termed a chemotherapeutic protocol and is formulated specifically for each individual case.  The treatment approach associated with the longest remission and survival times involves weekly  treatments for 2 months followed by biweekly treatments to complete a 6-12 month treatment period.  Alternative  options do exist.
  • Most cats tolerate chemotherapy very well.  It is our experience that the majority of pet owners are satisfied with their pet's quality of life while receiving treatment.  As lymphoma is not curable, our emphasis is placed upon this enhanced quality of life while undergoing therapy. Acceptable side effects may include loss of appetite, vomiting, diarrhea and listlessness for 1-2 days following treatment.  These effects are fortunately self-limiting. Occasionally, a chemotherapy dose reduction may be required to mitigate side effects.
What is the prognosis for dogs and cats with this cancer?
  • The likelihood of achieving remission and the duration of remission depends upon the location and stage of the cancer as  well as the treatment protocol administered.  For example, only 25-30% of patients with gastrointestinal lymphoma achieve complete remission. The duration of remission for patients with gastrointestinal lymphoma to whom chemotherapy is administered varies from 4 to 8 months, with some patients exceeding  one year of remission time.The most important prognostic factor in cats is their response to therapy.
  • FeLV status in some cases can be a negative predictor of survival time. Previous administration of prednisone may interfere with prolonged remission times. In general, patients with more widespread effects of the cancer do not respond as quickly nor for prolonged periods of time.
What is on the horizon for this cancer?

The use of radiation therapy in cats with gastrointestinal lymphoma has recently been reported. Newer chemotherapeutic agents are being tried as are different combinations of medications.

Mammary tumors are the third most common tumor type seen in the cat, and they account for approximately 20% of cancer in the female cat. These tumors arise from the mammary (breast) tissue and are typically malignant (invasive with a high chance of spreading). Most mammary tumors in cats are classified as adenocarcinomas. About 85% of mammary tumors in cats are malignant; meaning they are very invasive to the surrounding tissues and have a high rate of spreading to other areas of the body. Mammary cancer is often a disease of middle aged to older cats, with Siamese cats having a higher risk.

What causes this type of cancer in dogs and cats?
  • Hormonal influences are involved in the development of mammary cancer in cats. Several studies have found that cats that were spayed had a 40-60% reduced risk of developing mammary cancer.
What are the common signs of this cancer?
  • The first sign of this type of cancer may be a fluid filled or firm lump associated with the mammary gland, or discharge originating from the nipple. These masses do not tend to be painful but can be associated with increased grooming behavior if discharge is present.
How is it diagnosed?
  • A biopsy of the affected tissue is needed for making a definitive diagnosis. The majority of mammary tumors in cats are malignant in nature and very likely to metastasize (spread to other organs) early in the course of disease. The most common locations for this tumor to metastasize to are the local lymph nodes and lungs. Prior to any biopsy or treatment, palpation (manually feeling) of those local lymph nodes and chest radiographs are recommended to look for evidence of metastasis.
How is this cancer treated?
  • Surgery can be very effective at removing the masses, but the success of surgery is hindered by the invasive nature of the disease.  Due to this, an aggressive surgery is typically recommended, which involves removing all four mammary glands on the affected side (or both sides if needed), called unilateral or bilateral mastectomy. This procedure significantly reduces the chance for local re-growth of the tumor. It is important to evaluate the local draining lymph nodes during surgery due to the high risk of cancer spreading to those sites.
  • Since mammary cancer in cats typically invade the lymphatic system and spread to other locations, chemotherapy is recommended following surgery. Most effective protocols involve the use of a chemotherapeutic agent called doxorubicin alone or in combination with other drugs. Most cats tolerate chemotherapy exceptionally.
What is the prognosis for dogs and cats with this cancer?
  • The average survival time for cats with mammary cancer is variable and depends on several factors including size of the tumor, extent of surgery, the grade (how aggressive it is shown to be on the biopsy report), and whether additional therapy (chemotherapy is needed/used)
  • The average survival times range from 4 months to over 3 years depending on these factors.
What is on the horizon for this cancer?
  • As in women, the use of targeted therapies like Herceptin—a treatment that targets certain molecular and genetic defects found in cancer cells-- holds great promise for improving the outcome of therapy for the treatment of mammary cancer. In veterinary medicine there are currently two targeted therapies-Palladia and Masivet. There is currently a great deal of research looking for targeted therapies.

Mast cells are a type of normal white blood cell and are part of the immune system.  Mast cell tumors (MCT) comprise about 20% of all cutaneous (skin) tumors in the cat. These tumors can be benign (not cancerous) or malignant (cancerous and able to spread to other parts of the body). Over 90% of MCTs that occur in the skin of cats are benign while visceral (occurring in internal organs) MCTs may behave more aggressively.  This disease is seen mostly in middle-aged cats, and Siamese cats appear to be predisposed to getting this disease.

What causes this type of cancer in dogs and cats?
  • The actual cause of MCT is unknown. A genetic predisposition has been proposed due to the high incidence in Siamese cats. Mutations in certain genes (such as c-kit) have been studied extensively though a specific cause of this mutation has not been isolated.
What are the common signs of this cancer?
  • If your cat suffers from cutaneous (skin) MCT, you may notice small, firm, raised, hairless nodules on the head, neck, trunk, limbs, or other sites on your cat. They can intermittently be itchy or red and self-trauma can cause ulceration. If a mass is manipulated or “bothered”, a local allergic reaction canensue, and you may notice significant redness and wheal formation in the area of the tumor. This is due to the release of histamine and other inflammatory substances. Typically cats with skin MCT are otherwise healthy and show no signs of systemic illness.
  • Cats with the visceral, or disseminated, form of MCT (involving an internal organ or multiple organs) may show signs of systemic illness. They can be depressed, anorexic (loss of appetite), show weight loss, and vomiting. This visceral type is much more common in cats in comparison to dogs.
How is it diagnosed?
  • A fine needle aspiration (inserting a small needle into a mass) and cytology can be performed on skin masses to obtain a diagnosis of MCT. This can typically be done without any sedation and only takes several minutes. If the spleen is suspected to contain MCT or an intestinal mass is seen on ultrasound, a fine needle aspiration can also be performed, but may require some sedation.
  • The draining lymph nodes closest to the points of disease may be affected by some aggressive forms of this cancer.  If a lymph node is enlarged, it may indicate that the disease has progressed and spread. A fine needle aspiration and cytology can be used to determine if a MCT has spread to the lymph node.
  • Blood tests help determine the basic health of the body and organs. They can also identify mast cells in the blood (called a buffy coat test), which indicates that the tumor is spreading. Identification of low blood cell counts may indicate issues (such as bone marrow involvement or gastrointestinal ulceration) created by the growth of the mast cells.
  • A bone marrow evaluation may be recommended to evaluate for disease in the bone marrow. This procedure does require some sedation but is typically not painful.
How is this cancer treated?
  • Surgery is the treatment of choice for cats with the cutaneous form of MCT (as long as there are not too many MCTs for the surgeon to remove), since most of these tumors are benign and surgical removal is likely to be curative.
  • Surgery is typically not recommended for cats with disseminated MCT, unless the spleen is involved. It has been shown that cats with splenic MCT usually benefit from removal of their spleen, even when there is extensive disease such as bone marrow involvement.
  • Relatively little is known about the effectiveness of nonsurgical therapy for cutaneous MCTs in the cat. Responses to some chemotherapy medications have been reported and are typically recommended for cats with the malignant (cancerous) form of MCT.
  • Novel therapy with small molecular targeting drugs has shown great promise in fighting mast cell disease in cats. 
  • Drugs which block histamine receptors (such as cyproheptadine and famotidine) can reduce clinical signs of inflammation or stomach ulceration (by decreasing acid production induced by histamine).
  • Steroids are also useful for decreasing inflammation associated with these tumors.
What is the prognosis for dogs and cats with this cancer?
  • Many cats with the skin form of MCT can do very well for years with appropriate therapy.
  • Cats with the visceral form of MCT (spleen, intestine, liver) typically do worse than cats with the skin form, although the use of combination therapies (surgery, chemotherapy and TKIs) are allowing many cats to live well over a year.
What is on the horizon for this cancer?
  • The combination of small molecule inhibitors (Palladia and Kinavet for example) are being used more frequently in cats.
  • The use of combinations of chemotherapy and small molecule inhibitors is an active area of research.

Squamous cell carcinoma (SCC) is the most common oral tumor in cats. They can be extremely invasive (invading the bone of the jaw) but do not tend to metastasize (spread to other areas of the body) very rapidly. 

What causes this type of cancer in dogs and cats?
  • According to research, the risk of developing oral SCC may increase significantly with the use of flea collars, high intake of canned food (especially canned tuna fish), and exposure to household tobacco smoke.
What are the common signs of this cancer?
  • Most cats present with a mass in the mouth that may be ulcerated (an open and bleeding wound). Your pet may experience increased salivation, dropping food out of the mouth when eating, facial swelling, weight loss, bad breath, pain, and/or a bloody nose.
How is it diagnosed?
  • All cats that are suspected of having an oral SCC should have bloodwork performed to evaluate overall health.
  • Biopsy of the abnormal tissue mass is the most definitive way of obtaining a diagnosis. This always requires an anesthetic procedure. There are 2 ways of obtaining the tissue sample for biopsy: excisional (removing the entire mass if possible) or incisional (taking a representative piece of tissue from the mass). SCC in cats often invades into the bone, so an excisional biopsy can be difficult without a surgical procedure.
  • While your cat is under anesthesia for the biopsy procedure, other tests may be recommended. These may include skull radiographs (x-rays) and/or a CT scan. These two tests can evaluate the degree of bony involvement, as well as help determine how aggressive a surgical procedure would need to be in order to try and remove the entire tumor.
  • Even though SCC in cats tend to have a low rate of metastasis (spreading), it is important to evaluate the local lymph nodes (typically the lymph nodes under the jaw) and the lungs (with radiographs) for metastasis prior to starting any therapy.
How is this cancer treated?
  • Surgery is the treatment of choice but can be very difficult due to the aggressiveness and invasiveness of this tumor type. Since oral SCC typically involves the bone, part of the jaw typically needs to be removed. If the tumor is located on the lower jaw and towards the front of the mouth, it can be fairly easy to remove and most cats will have a good quality of life post-operatively. If the mass is located anywhere else in the mouth, the surgery can be much more difficult and sometimes cats need a temporary feeding tube to maintain adequate nutritional intake.
  • Radiation therapy or chemotherapy alone is generally ineffective in the management of most cats with oral SCC. However, the combination of radiation therapy with certain types of chemotherapy can improve the response rate, quality of life and overall survival time. 
What is the prognosis for dogs and cats with this cancer?
  • Local disease (the mass in the mouth) eventually becomes very difficult to control (if no therapy is undertaken) and is the most challenging problem with this disease.
  • Cats that have SCC on their mandible (lower jaw), closer to the front of the mouth, and have had an aggressive surgery, tend to have longest survival times.
  • The average survival times for cats with oral SCC with that receive no treatment is usually around 3 months.
What is on the horizon for this cancer?
  • There are currently a few studies evaluating how effective the combination of radiation therapy and targeted chemotherapy is in treating this disease. Because this disease is very resistant to traditional therapy, there are many researchers looking for new modalities with which to treat this cancer.

Adenocarcinomas are one of the three most common tumors that arise in the gastrointestinal tract (stomach, duodenum, jejunum, ileum and colon) of cats--the other two being lymphoma and mast cell tumors. These tumors typically occur in older cats and there is a male predilection. Both Siamese cats and Domestic Shorthair cats have been reported to have a higher incidence of this disease.

What causes this type of cancer in dogs and cats?
  • There are no known causes of this cancer, although carcinogens on the fur that are ingested when the cat grooms have been implicated in other gastrointestinal cancers (lymphoma).
What are the common signs of this cancer?
  • The most common signs are vomiting, weight loss and anorexia (loss of appetite). The vomitus or stool may contain blood.
  • Abdominal distension or a palpable mass in the abdomen may also be detected.
How is it diagnosed?
  • Diagnosis usually starts with a good physical examination, CBC/chemistry and abdominal ultrasound. Ultrasonography has enabled veterinarians to detect tumors at a smaller size than those detected by radiographs (x-rays).
  • The diagnosis is confirmed by getting a cytologic (with a needle) or biopsy (with surgery or endoscopy) sample.
How is this cancer treated?
  • One of the most important treatments is surgical removal of the intestinal mass. This is helpful even if the tumor has already spread (metastatized) as cats treated with surgery live longer even in the face of metastatic disease.
  • Most cats with this disease have metastasis at the time of diagnosis, and therefore chemotherapy is highly recommended for most cats with this disease.
What is the prognosis for dogs and cats with this cancer?
  • Many cats with intestinal adenocarcinoma can live well beyond a year if treated with surgery and chemotherapy. Their quality of life is typically extremely high.
What is on the horizon for this cancer?
  • New combinations of standard chemotherapy drugs are being used to try and more effectively treat this disease.
  • The use of small molecule drugs/ tyrosine kinase inhibitors (TKIs) are being investigated in the treatment of this disease.

Vaccine associated fibrosarcomas (VAS) are tumors of connective tissue that develop at sites of previous vaccinations. Vaccine associated fibrosarcomas (VAS) are thought to develop in 1/1000 to 1/10,000 cases. The time it takes for a tumor to develop after a vaccine can be anywhere from 4 months to over 10 years. These tumors typically behave in a very aggressive fashion. These tumors can extend up to 5 cm beyond the margins of the tumor and there is evidence of metastasis (disease that has spread) at diagnosis in approximately 12% of the cases.  These tumors invade through tissue planes sending out projections of tumor cells much like the roots of a tree. Due to this fact, complete surgical excision can be difficult and the mass that is visible on the skin is usually only the “tip of the iceberg” as there can be a significant amount of disease below the surface. VAS are more locally aggressive (30-70% recurrence rates) and systemically aggressive (~25% metastatic rate) than fibrosarcomas that are not caused by vaccinations.

What causes this type of cancer in dogs and cats?
  • Vaccines–most commonly Rabies and FeLV, but can occur secondary to any vaccine.
  • Growth factors such as  platelet-derived growth factor (PDGF) may play a role in VAS.
What are the common signs of this cancer?
  • Patients are often asymptomatic (show no clinical signs) aside from a mass that is noticed by the owner
  • Clinical signs such as pain or limping  can occur depending on the size and location of the mass
  • These tumors can also become  open and ulcerated with bleeding and infection possible
How is it diagnosed?
  • CBC/chemistry panel/urinalysis and 3 view thoracic (chest) radiographs
  • CT imaging of the tumor and the  surrounding area to determine the extent of the mass as well as if there is any invasion into the surrounding tissues
  • Aspiration and cytology can help to classify a mass as a sarcoma but histopathology (biopsy) is needed to definitively diagnose a VAS
How is this cancer treated?
  • Aggressive surgery is the most important part therapy
  • Ideally, a CT scan should be performed before the surgery to assess the extent of disease and plan complete surgical removal. A CT scan can sometime show double the amount of disease that can be detected on physical examination.
  • Aggressive surgical resection with wide and deep margins (3cm laterally and 1 fascial plane deep) should be obtained. Aggressive resection can include amputation if the tumor is on a limb. With each subsequent surgery, the chances of long-term control  decrease.
  • An incisional biopsy is recommended to obtain a diagnosis prior to CT scan so that the surgeon can plan for a complete surgical excision
  • Due to the aggressive behavior of these tumors surgical excision alone typically does not result in  long-term control, so adjuvant (additional) treatment with radiation therapy is recommended to help control the local disease.
  • Side effects from radiation are mild and consist of local dermatitis/sun burn like effect that resolves within 2-3 weeks with supportive care
  • Because VAS have a higher rate of metastasis (spreading) than non-vaccine associated sarcomas treatment with chemotherapy is recommended after surgery and radiation therapy
What is the prognosis for dogs and cats with this cancer?
  • Aggressive surgery followed by radiation therapy can result in median survival times of well over 2 years.
What is on the horizon for this cancer?
  • Recommendations such as standard vaccine administration sites for each vaccine, giving vaccines on distal extremities, and the use of non-adjuvanted vaccinations are just some of the recommendations that have been made to try and prevent this tumor from occurring
  • There is also the 1-2-3 rule for a vaccine site reactions. This states that any vaccine site reaction/swelling that has been growing for more than 1 month, is greater than 2cm, or is still present after 3 months should be removed and biopsied.