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Cancer and Chemotherapy

| March 1, 2017
Cancer is a mass of tissue that is characterized by persistent, excessive, and disorganized cell growth that is unresponsive to normal control mechanisms.

Cancer is a mass of tissue that is characterized by persistent, excessive, and disorganized cell growth that is unresponsive to normal control mechanisms.


Cancer is a mass of tissue that is characterized by persistent, excessive, and disorganized cell growth that is unresponsive to normal control mechanisms. Why this happens, in most cases, is not yet known. In a normal situation healthy cells grow, divide and replace themselves in a systematic fashion. This natural process helps keep the body in good repair and slows the effects of daily wear and tear. Cancer cells, on the other hand, do not develop normally. They continuously multiply and divide and never mature properly to reach a resting state. In short there is no order or system to their replication. Many cancers do not directly cause problems to the body but merely occupy more space than they are naturally allotted. They crowd out the vital functions of other parts of the body and may cause complications due to this interference. Other cancers are “functional” in that they produce hormones or other substances that affect the body.

The following are commonly used terms in cancer medicine:


  • Tumour: simply means a “swelling,” which may or may not represent cancer.
  • Benign tumours: have many normal growth characteristics. They do not “spread” or invade other organs. They may, however, compress body organs or tissues by virtue of their size. Surgical removal is usually curative.
  • Malignant tumours: often have rapid, irregular growth characteristics. These tumours can invade normal, local tissues, as well as spread to other tissues (especially the liver and lungs). New tumours can grow at these secondary sites, eventually causing the demise of the patient.
  • Metastasis: the process whereby a tumour spreads to secondary sites. These new tumours are referred to as “”metastatic”,” or “metastases.”
  • Oncology: refers to the study of cancer, including biological behaviour and treatment.
  • Remission: denotes a decrease in tumour size (often called “tumour burden”) over time. Remission time is the length of time in which the cancer is under control. Currently, treatment of cancer in animals can often result in fairly lengthy, good quality remission times. That still means that for many types of cancers, their return is inevitable.

As a result of improved owner and veterinary care, pets are living much longer and are thus more susceptible to diseases of old age, such as tumours. If your pet is thought or known to have cancer, a consultation with a veterinarian experienced in oncology can provide you with valuable information regarding treatment options and expectations.

Cancer can often be diagnosed on the basis of a procedure called fine-needle aspiration. This is a minimally invasive, non-painful, technique that involves inserting a needle into the tumour, aspirating a few cells out, and smearing the cells on a slide for a pathologist to evaluate under a micro­scope. When cancer is diagnosed (or suspected), further diagnostic tests can be performed to stage the cat’s cancer. Staging allows your veterinarian to educate you further about your cat’s disease, allowing you to make informed decisions regarding treatment. A thoracic radiograph will be performed to look for metastasis. A complete blood count, biochemistry profile, and urine analysis will be obtained to assess your cats’ overall health status. An ultrasound examination of the abdomen may also be performed to search for metastasis. Other tests may be recommended, depending on individual circumstances.


Chemotherapy and/or surgery are the two most important treatment modalities in veterinary cancer medicine. A combination of therapies may also be indicated in certain cancers. Some cancers require a specific, brief number of treatments, while others require ongoing treatment to maintain remission.

Surgical removal of tumours is a very common and valuable approach for solid tissue tumours. It can sometimes be curative on its own, if the disease process is localized and detected very early.

This consists of the use of a radioactive beam to damage and/or kill malignant cells in a localized area. It can offer good quality remission times for many types of tumours, but usually not a cure. Animals are surprisingly tolerant of radiation therapy

The use of a drug or chemical to treat any illness is chemotherapy, but this term commonly refers to the use of drugs in the treatment of cancer. The goal of chemotherapy in companion animals is either to increase the life span or to improve the quality of life for the animal with cancer. All of the drugs currently given to animals are human anti-cancer drugs. Fortunately, many of the negative consequences of their use in human medicine are not experienced in veterinary medicine.

Commonly asked questions about chemotherapy:

  • How does chemotherapy work? Anti-cancer drugs work by blocking cell growth and division. Different drugs interfere with different steps in these processes. In many cases, a combination of drugs is the most effective way to kill cancer cells.
  • How is chemotherapy given? Most anti-cancer drugs are given by mouth or by injection. The route chosen depends on the type of drug and the type of cancer.
  • How long will my pet receive chemotherapy? The length of time and frequency of drug administration will depend on the kind of cancer being treated and how well the therapy is tolerated by the patient. Treatment may be given daily, weekly, or monthly.
  • Am I at risk of exposure to these drugs? Yes. Most anticancer drugs are very potent and must be handled with care. Some are “carcinogens’” and can cause cancer with prolonged exposure. With orally administered drugs, it is important that the pills or capsules are kept out of reach of children in childproof containers. When handling these drugs, the owner should wear latex or polyvinyl gloves to avoid unnecessary exposure. With oral and injectable drugs, the cat’s urine and faeces may be contaminated with active drug compounds for several days after administration.
  • Will my pet experience side effects? Maybe. Veterinarians try to choose drug doses and combi­nations that cause the fewest side effects. Ideally, the animal receiving chemotherapy does not even realize that he or she is ill. The drugs used in chemotherapy, however, are ex­tremely potent and side effects can occur. The potential for side effects must be balanced against the benefits of the chemotherapy and the side effects of the cancer if left untreated. Choosing chemotherapy for your pet is an individ­ual decision.


Veterinarians who treat animals for cancer use many of the same chemotherapy agents that human oncologists use. Yet, in many ways the experience for pets seems very different. Why? For one thing, dosages of chemotherapy agents used in animals tend to be much lower than those used in people. Humans are given the highest doses possible, the consequences of which may require bone marrow transplantation, extended hospitalisation, and numerous costly medications-all with good cause. However, for veterinary patients, this process would be unacceptable and cost prohibitive for most owners. The general quality of life for many veterinary cancer treatment patients can be surprisingly good and very close to normal. Most of the time they can maintain their normal activities and have fun with the families that love and care for them.

Side effects arise because the normal cells in the body are also exposed to the anticancer drug. The most sensitive normal cells are found in the blood, gastrointestinal tract, skin, and reproductive system. The good news is that the normal cell lines can almost always regenerate themselves, while the less well-organised malignant cells suffer great damage. Potential side effects include infection, bleeding, decreased appetite, vom­iting, diarrhoea, thin hair coat or skin colour changes, and sterility. Hair loss, in contrast to humans, is uncommon in cats on chemotherapy. Rare side effects associated with specific drugs include bladder discomfort, kidney damage, and heart fail­ure. The most serious side effect is overwhelming infection leading to death.

There are various reasons why chemotherapy is better tolerated in pets, but probably the most important factor is psychological. Your cat does not know he has cancer. He also does not know the drugs make people sick, so he does not anticipate that he will be sick. Human cancer patients suffer from a phenomenon called anticipatory vomiting, but cats do not have this problem.

It is not a “given” that untoward side effects will occur in any one patient. In fact, the majority of patients complete their therapies without major complications. However, if they do occur you should be prepared to recognize them and take appropriate action. Over time, the tendency is to have less frequent side effects, as the individual animal’s sensitivity to the drug agents become known, the treatments are less frequent, and the cancer is in remission.

The most common side effect reported by owners is that the pet seems to be “off” for a day or two. This might mean that the pet has slightly less energy or seems less excited than normal about eating. Less commonly, the pet may skip a meal or two, have one episode of vomiting or diarrhoea, or seem lethargic. Unfortunately, there is no way to predict which pet will develop the most serious reactions. The animal receiving chemotherapy needs to be watched closely and taken to his veterinarian at the first sign of illness. Chemotherapy will suppress your pet’s immune system and make him more susceptible to infections. These infections generally arise from bacteria that normally live in the intestinal tract and on the skin and not from the environment. Signs of an infection may include loss of appetite, vomiting, diarrhoea, decreased activity, or depression. Phone your veterinarian immediately if your pet appears ill while receiving chemo­therapy. These signs are usually only brief reactions to the drugs but prompt treatment can often prevent more serious side effects from developing.


One of the most important goals of cancer treatment in animals is to maintain as much of the pet’s normal lifestyle as possible. This can often mean that once a pet has recovered from cancer surgery, and/or passed the initial phase of chemotherapy, restrictions on activities are very few, and will be discussed by your veterinarian.

It is now known that cancer results in significant alterations in carbohydrate, protein, and fat metabolism. Research findings have lead to the creation of a specific dietary program that depletes cancer cells of their required nutrients. A specific prescription diet is available from your local veterinarian and is comprised of limited quantities of simple sugars, modest amounts of complex sugars, modest amounts of highly digestible proteins, and calculated amounts of certain types of fat (including omega-3 fatty acids which have a negative effect on tumor growth, and improve survival times).


This is a difficult question to answer. Every situation and client-pet relationship is different and must be dealt with individually. If it were ever obvious that therapy was not working, or that the pet was indeed experiencing pain or discomfort, then your veterinarian is ethically obligated to inform you. Most pets do indeed appear to enjoy their extended life period and do not even realize that they are “ill.” The owner must, however, believe that they are doing the right thing for their pet and realise that this therapy is unique in that it can successfully prolong the cat’s life


Some of the common tumours that affect the cat are lymphoma, squamous cell carcinoma, and mammary gland tumours.

Lymphoma is a cancer of a specific white blood cell called the lymphocyte. Lymphocytes are found throughout the body in blood and tissues and act to protect the body from infec­tion. Lymphocytes are the major cells found in lymph nodes or “glands.” In lymphoma, the cancer cells invade and destroy normal tissues. The most common site for lymphoma is the lymph nodes, but lymphoma cells, like lymphocytes, can grow anywhere in the body. In most cats with lymphoma, the cancer cells are present in multiple lymph nodes and tissues.

Of all the tumours, lymphoma accounts for approximately 30% of all feline malignancies and may be associated with either feline leukaemia virus or feline immunodeficiency virus infection. Chemotherapy is the treatment of choice for lymphoma. Surgery and radiation therapy are less useful in lymphoma because these treatment methods attack cancer cells at only one site.

The goal of chemotherapy for animals with lymphoma is to induce a complete ‘remission” by killing the cancer cells. Animals with lym­phoma that are in complete remission look like normal animals by all accounts. They do not have any signs of cancer, and all masses or lumps have disappeared. They eat, drink, and play just as they did before they developed cancer. Unfortunately some of the cancer cells can survive in an animal in complete remission, but the numbers are too small to detect. Eventu­ally, these few cells will grow and the cancer will become evident again. When this happens the animal is said to be “out of remission.” Sometimes a second remission can be achieved with additional chemotherapy. Eventually, the can­cer cells will become resistant or insensitive to all drugs and results in the death of the cat.

Although chemotherapy does not cure cats with lymphoma, in most cases it does extend the quantity and quality of life. About 80-90% of cats with lymphoma attain a complete remission with an average survival of I year, and 25% live for more than 2 years.

Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) has two distinct presentations in the cat. The first is a lesion of the nasal plane, ears, or facial skin in white or lightly pigmented cats and is associated with sunlight-induced damages. Diagnosis of facial SCC is often delayed for months after lesions appear because the owners or veterinarians assume they are healing fight wounds. Facial SCC occurs in outdoor cats and is prevalent in South Africa because of our sunny location. These tumours are locally invasive and slow to metastasize. Regional lymph nodes are the most common site for metastasis but pulmonary metastasis is extremely rare. Treatment options include surgical excision, radiation therapy, or local chemotherapy. Adequate surgical resection requires very wide margins and recurrence is common despite seemingly aggressive surgery. Radiation therapy and local chemotherapy can result in complete remission if used early on in the disease.

The second common presentation is oral SCC and is the most common oral tumour of the cat. It often occurs on the floor of the mouth precluding surgical excision. It is locally invasive and slow to metastasize, however cats often stop eating, due to the presence of the tumour or secondary bacterial infections. Radiation therapy in conjunction with chemotherapy has been described for oral SCC, however survival times are usually less than 4-6 months. Palliative therapy, including analgesics, tube feeding, and antibiotics for secondary infections, allows many cats to thrive in spite of advancing local disease. In cases where the tumour is small and can be treated with aggressive surgery, the prognosis is better.

Mammary Gland Tumours
Mammary gland tumours (MGT) are reported to have a prevalence of approximately 25/100,000 female cats making MGT the third most common tumour of cats. Unlike dogs, where only 50% of MGT are malignant, almost all feline MGT are malignant. Clinical signs are attributable to presence of the MGT, which typically affect the cranial or caudal mammary gland pairs. One study reported that cat MGT were present 7 months before the owners consulted with a veterinarian. Client education to allow early intervention is thus very important.

Treatment is aggressive surgical resection. The surgery of choice is bilateral radical chain mastectomy. Cats undergoing radical chain mastectomy have a significantly longer median disease free interval (575 days) compared to cats undergoing conservative surgery (325 days). The most significant prognostic variable may be tumour size at the time of surgery. Cats with tumours > 4 cm in diameter have a median survival of 6 months, whereas cats with tumours < 2 cm in diameter have a median survival of approximately 4 years. The role of chemotherapy from MGT is unknown in cats, but because of the aggressive nature of feline MGT, it may prove to be beneficial.

Vaccine Associated Sarcoma
Vaccine associated sarcomas (VAS) are recent phenomena in cats. The first descriptions of vaccine site inflammatory reactions came in the mid-1980s in North America. This coincided with mandatory rabies vaccine laws for cats and a change from the use of intramuscular rabies vaccines to subcutaneous preparations. The types of VAS may include fibrosarcoma, malignant fibrous histiocytoma, rhabdomyosarcoma, osteosarcoma and undifferentiated sarcoma. A common feature of these rapidly growing tumours is the presence of a necrotic centre and prominent inflammation. VAS may develop from 3 months to 3 years after vaccination. The incidence has been estimated to be as high as 1/5,000 cats vaccinated.


Copyright & Credit:

Source: Dr Remo Lobetti
BVSc (Hons) MMedVet (Med) Dipl. ECVIM (Internal Medicine) Veterinary Specialist Physician

Dr Remo Lobetti Feline Infectious Peritonitis

Bryanston Veterinary Hospital
6 Ballyclare Drive

Tel: +27 11 706-6023/4/5
Fax: +27 11 706-5801
Emergencies: +27 11 706-6023e

Photo copyright and courtesy: Portraityogi


Category: Feline Health, Feline Health and Care, Feline Resources

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