Chemotherapy and your pet

The diagnosis of cancer is stressful for pet owners, and the prospect of chemotherapy treatments can be equally difficult. However, the fear that animals will spend most of their time sick from chemotherapy is unwarranted. Knowing how anti-cancer chemotherapy drugs work and what to expect from the treatments can help pet owners decide on whether such therapy is appropriate for their pets.

When do we use chemotherapy to treat animals with cancer?

Chemotherapy may be used as the sole treatment for certain cancers or may be used in combination with other treatment modalities, such as surgery and radiation therapy. Chemotherapy is likely to be recommended for cancer with a high likelihood of spread to other areas of the body, for tumours that occur at more than one site or for tumours that cannot be removed surgically. In some cases, chemotherapy can be used to shrink large tumours prior to surgery. For cancers that are high-risk for spread early in the course of disease, chemotherapy can be used after surgery to help prevent or delay local regrowth or the establishment of cancer in other parts of the body.

How does chemotherapy work?

Chemotherapy drugs attack cells in the process of rapid growth. Individual drugs may work through many different mechanisms, such as damaging a cells genetic material (DNA) or preventing a cell from dividing. However, chemotherapy drugs cannot distinguish between cancer cells and normal cells. All rapidly dividing cells are potentially affected by chemotherapy. This accounts for most of the side-effects seen with chemotherapy. Fortunately these normal tissues continue to grow and repair themselves, so the injury caused by chemotherapy is rarely permanent.

What are the typical side-effects of chemotherapy?

Compared to people, pets experience fewer and less severe side-effects. The main reason for this is that we use lower doses of drugs thus causing less toxicities. Pets also do not “know” that they have cancer or that they are receiving chemotherapy. They thus do not suffer from known conditions found in people such as “anticipatory nausea and vomiting”.

The normal tissues that are most sensitive to chemotherapy are the intestinal lining, the bone marrow (which makes red and white blood cells) and hair follicles.

Most cases of intestinal toxicity are mild and usually resolve on their own or with medication given at home. Some cases may require hospitalisation with more specific treatment but this is very rare. Suppression of the bone marrow may cause a drop in the white blood cell count leading to increased susceptibility to infection. Severe cases require hospitalisation with intensive treatment, but in most cases the white blood cells are checked on a weekly basis or before any chemotherapy is administered so as to pre-empt any potential side-effects.

Hair loss (alopecia) is not a common side-effect in pets. Only hair that is continually growing, is affected by chemotherapy, so only certain breeds may be affected (poodles and certain terriers). Whiskers, especially in cats, often fall out with chemotherapy treatment, but re-grow once chemotherapy is stopped.

There are many different types of chemotherapy agents and each has a different likelihood of causing side effects. If your pet is treated with drugs known to cause certain side effects, we will prescribe medications to help prevent these complications. In addition we will give you instructions on what to do if a problem should arise. We seldom see severe side effects as described and with proper management, most animals recover uneventfully from chemotherapy. Please keep in mind that any animal can have an unexpected reaction to any medication.

How much does chemotherapy cost?

Treatment of cancer with chemotherapy can be expensive. It involves the use of the same medications used to treat human cancer patients, and many of these medications are expensive. The exact cost of chemotherapy varies with the size of your pet, the number of treatments and the particular medications being administered. We may need to refer you to a veterinarian that specialises in Oncology to discuss the most up to date options available for your pet's particular type of cancer and they will determine the projected cost of your pet's individual treatment.

How is chemotherapy given?

How a chemotherapeutic drug is given, how often it is given and how many treatments are given, varies from patient to patient. The type of cancer, the extent of disease and the general health of the patient help to formulate a treatment protocol appropriate for each individual pet.

Some drugs are oral medications (tablets) you can give at home. Others are single intravenous injections that require hospitalisation during the day and others are slow intravenous infusions which generally require hospitalisation for one or two days.

The treatments are typically repeated from weekly to once a month. Blood tests may be needed to monitor the effects of the chemotherapy between treatments.

The duration of chemotherapy also varies. Some patients need to receive chemotherapy for extended periods (several months), whilst others may only require 2-3 treatments.

What can be expected from chemotherapy?

In some cases we are unable to cure our veterinary cancer patients. Our goal is therefore to improve a pet’s quality of life. To this end, chemotherapy can be used to minimise the discomfort caused by a tumour or to slow or arrest the progression of the disease.

The decision whether to pursue chemotherapy treatments can be complex. Medical information, practical concerns and financial responsibility all play a role in this decision. We encourage you to empower yourself with knowledge and to discuss your concerns with us when making this decision.

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