Chemotherapy - Basic Information for Pet Owners
Chemotherapy refers to any drug given for therapeutic reasons. Technically, antibiotics are chemotherapy. However, common use has changed the term to refer almost exclusively to treating cancer. In this context, chemotherapeutic agents (chemotherapy drugs) are those that kill cancer cells. The best chemotherapy drugs are those that kill only cancer cells, and leave normal body cells alone. Unfortunately, these drugs are rare to non-existent. There are always civilian casualties' in the was against cancer.
Chemotherapy is the single most effective method of treatment for some cancers (like lymphoma or lymphosarcoma) and offers an opportunity for extension of life along with good quality of life during therapy. We will also recommend chemotherapy after surgical removal of some tumors. There are two reasons for this: to stop the recurrence of the tumor in the same location, and to inhibit its spread to distant parts of the body (a process called metastasis). Although we do not offer radiation therapy at our clinic, chemotherapy is sometimes used in conjunction with radiation in order to make the radiation more effective at killing the cancer cells.
Cancer cells tend to be rapidly replicating (reproducing), which is why cancers spread so quickly, and why tumors can grow so rapidly. The drugs used to treat cancers affect rapidly growing cells the most. They are often drugs that interfere with the cell's DNA, and so kill the cell when it tries to divide. In order to be effective, these drugs need dividing cells like those present in tumors.
The collateral damage happens mostly to other rapidly dividing cells in the body like the bone marrow and the lining of the stomach and intestines. These cells are the ones hardest hit by chemotherapy drugs, and the effect on these cells are what cause the problems we associate most with chemotherapy.
The most common adverse effects of chemotherapy are on the gastrointestinal tract. We typically see nausea, vomiting, and possibly diarrhea. Because most animals are not good at telling their owners that they feel nauseated, and because most owners are unaware of the subtle signs of nausea, we usually dispense an anti-nausea medication that is given at home for a day or two after each chemotherapy treatment. We give it to patients in the hope of forestalling any vomiting, or helping if the pet does experience nausea. A few key signs of nausea are lip-licking, drooling, and lack of appetite.
The most serious effect of chemotherapy drugs is their effect on the rapidly dividing cells of the bone marrow. The marrow contains undifferentiated blood cells that will develop into the many different cells that populate normal blood. We are concerned mostly with the cells that are the "parents" of the white blood cells. White blood cells fight infection, and a serious depletion in their numbers, as can happen when the bone marrow is affected by chemotherapy drugs, can leave the pet vulnerable to serious infection. Sometimes this infection can become systemic and enter the bloodstream, a condition called sepsis. Sepsis is a potentially life-threatening condition.
A much less common problem is hair loss. Few dogs experience real hair loss when undergoing chemotherapy. The exception to this is a breed with continuously growing hair, like the Lhasa Apso, Poodle, Shih Tzu, Old English Sheepdog, Puli, Maltese, and some Schnauzers. We will sometimes see significant hair loss in these dogs early on in the treatment protocol. This hair will grow back once chemotherapy stops, or even when the frequency of drug administration is decreased. Also, not all dogs of these breeds experiences hair loss; it is an individual thing.
An additional adverse reaction that can occur with some types of chemotherapy drugs is an extreme tissue reaction to the drug if it accidentally comes in contact with the tissues around or outside of a vein. If the drugs leak out of the vein, or are accidentally injected outside of the vein, severe necrosis (death) of the surrounding tissue can occur. Needless to say, this is a very infrequent occurrence as every precaution is take to prevent it, including using long intravenous catheters and sedating pets who are at risk of dislodging a catheter during chemotherapy administration. The drugs most commonly associated with this tissue reaction are doxorubicin, vincristine, and nitrogen mustard.
Other side effects are quite drug-specific. Doxorubicin treatment carries with it a risk of cardiotoxicity (heart damage). The platinum agents (cisplatin and carboplatin) can be very toxic to the kidneys. Cyclophosphamide can cause sterile cystitis (bladder inflammation). Vinca alkaloids (vincristine, vinblastine) and platinum agents can be neurotoxic. L-asparaginase and many other drugs can cause acute allergic and hypersensitivity reactions. CCNU (Lomustine) and other drugs. can be toxic to the liver.
All patients undergoing chemotherapy will need regular blood testing.The majority of the tests will be checks of the blood cell counts. We will also need to evaluate the liver and kidneys on a regular basis ("regular" depending on the type of protocol being used). As a rule of thumb, blood counts are done 7-10 days after the dose of chemotherapeutic drug. There are variations on this, and you will be informed of the schedule for your pet before we start his or her treatment.
Quality of Life
Chemotherapy is meant to prolong life, not to prolong dying.
It is not cruel or inhumane to opt for cancer chemotherapy for your pet. Most animals that undergo chemotherapy have a very good quality of life. They are happy, eating and drinking, and interacting with their families. Most have normal energy levels most of the time. There may be a day or two right after the chemotherapy treatment day where the pet feels "off", but we try to minimize any of the detrimental chemotherapy effects as much as we can. Also, we can stop at any time. If you, the pet's owner, feel that his or her quality of life is poor during chemotherapy we can stop giving the drugs. Many owners enter into chemotherapy with some trepidation, and discover that the reality is nowhere near as bad as their expectations.
Cancers are rarely cured. In most cases we hope for remission of the tumor, or remission of the cancer effects that are making the pet feel sick. Some cancer types offer the hope of long remission times, but there are always variations. We have to face the sad reality that most pets who have cancer, even if they have chemotherapy, will eventually relapse. We will be faced with the decision of when and whether to euthanize. As always, this decision should be made by loving owners based on their knowledge of their own pet, and with his or her quality of life always in mind.
Many clients are concerned that their pets are experiencing pain with their cancer. Control of pain is one of our top priorities, not only from a humane aspect but because animals in pain do not respond as well to therapy and do not heal as well. We work with all of our clients to optimize pain relief for their pets and minimize discomfort.
Cancer patients need to eat to stay strong and have the resources to handle chemotherapy and the effects of the cancer. We encourage all owners to encourage their pets to eat. Warming the food and providing a stimulating environment is sometimes all that is required. For other patients, the best was to get nutrition in is via a feeding tube. These can be minimally invasive and extremely well tolerated. Sometimes appetite stimulants will help. Supplemental amino acids, omega-3 fatty acids and a good vitamin and mineral supplement (such as Canine Plus) also assist in the patient's recovery.
Most chemotherapy drugs are given by intravenous injection or infusion through an intravenous catheter. This means that an intravenous catheter is placed and secured. The chemotherapy drug is injected through the catheter with a syringe, followed by a copious flushing with saline. Drugs that take longer to infuse (like doxorubicin) will be delivered via a regular intravenous drip over a period of time.
Depending on the drug (and that can vary by the week in some chemotherapy protocols) you should plan on the entire visit taking about 30-45 minutes (for injections or rapid infusions) or up to 3 hours for longer infusions (typically doxorubicin). You will be informed of the appointment length when you book.
We do chemotherapy treatments most Mondays, Tuesdays, Thursdays and Fridays.
The cost of the treatments will depend on the medications. Chemotherapy drug costs vary wildly, from $20 per treatment to $750, depending on the drug and the size of the patient. There are also attendant costs for the actual procedure, whether it involves an IV catheter and injection or a full intravenous setup. You will be informed of the cost, if you so desire, before starting any chemotherapy protocol.
Chemotherapy can last anywhere from a few weeks to several months to lifelong, depending on the type of cancer being treated and the therapy protocol used.
It is always a good idea that you keep a diary of your pet's chemotherapy treatment. Noting the dates and drugs used for each session, as well as the dates of follow up lab testing is very useful to anyone treating your pet in an emergency. Also have a written record of any oral medications you may be prescribed, their doses and frequency.
Dr Wilkie is available by telephone after hours until 9 pm most nights (cell phone number is on the clinic answering machine, 604-926-8654). If there is no answer, or you have an emergency after 9 pm you are advised to contact the Vancouver Animal Emergency Clinic, 604-734-5104. If need be, they can contact Dr Wilkie at home.
Some emergencies can be directly attributable to the chemotherapy treatment. Sometimes you just have "regular" emergencies. In either case the veterinarian seeing your pet will need to know his history in order to treat appropriately and choose medications that will not interfere or worsen the effects of the chemotherapy.
Take the bottles of any medications that have been prescribed for your pet with you when you go to the emergency clinic.