VetInfo Digest     July 2001

This Month:

Why Doesn't My Vet Like My Breed?

Cancer Therapy:

The Basics

ProHeart 6 (tm)

This month's note:

I started out this month trying to write the VetInfo Digest as an update on the most recent recommendations for cancer therapy in pets. It seemed like a good idea to try to compile a list of the current treatment protocols of the common cancers and put them all in one issue. Cancer will affect most pets and some oncologists estimate that cancer may account for 50% of the deaths in geriatric dogs and approximately 40% of deaths in older cats. However, as I tried to compile this list it became clear that it was necessary to explore the general aspects of cancer therapy a little in this issue and then try to put the specifics of therapy for individual cancers in the next issue.

I think it is important to keep in mind that cancer therapy, like many medical treatments, is not an absolute science. The definition of a successful therapy for cancer is different among different veterinarians and different pet owners. Some pet owners would trade months of life span for a few weeks that their pet could feel really good. Other pet owners are willing to risk weeks of discomfort for their pet against the hope that the end result might be a cure or at least a very long remission. These attitudes are both valid. The problem lies in choosing when to pursue one option over the other and how to provide the maximum level of comfort regardless of the method chosen. For this reason, this month I want to try to explain how to care for the patient who has cancer and next month to talk about how to attack the cancer itself.

Why Don't Vets Like My Breed?

Just about every day someone asks me what I think about a certain breed of dog or cat. Invariably, I say something like "Well, they're nice pets, but they have a tendency to get cataracts, allergies, pancreatitis..," and so on. Sometimes, by the time I get done listing the medical problems that I can remember as the prevalent ones for the breed, the person is either mad at me or has come to the conclusion that the breed isn't a good one.

The angry group starts in with "What have you got against my breed?" The truth is that there are only a couple of dog breeds that I really think are so sickly or have so many behavioral problems that I feel bad when someone comes to the clinic with one of them. And even among these breeds there are many members who are healthy or who make great pets despite the general temperament of the breed. So I don't really have anything against their breed, I am just answering the question the way a veterinarian tends to answer the question, by listing the problems that I know to exist in the breed.

The second group almost always asks, "Well then, what do you think about "X" breed?" About the time I answer, "Well, they have this problem and that problem and...," the people usually catch on and ask "Is there any breed without problems?" The answer to that question is easy. No, there is no breed without problems.

Why do vets only think of the problems in a breed? I think that the answer lies in the way that our memories categorize things. It would be very hard for me, or for any vet to remember all the similarities between the breeds of dogs and cats. It is even hard to remember all the similarities between the two species. It is much easier to remember the differences, which in most cases are the problems that one breed has compared to the mythical "normal" breed. When I can do this, I can remember to check for things that are more likely to be a problem in this breed than in other breeds. Unfortunately, though, this thinking also lends itself to answering questions about specific dog breeds with a list of problems rather than a list of positives.

Don't get excited if your vet tells you about the tendency for dominance aggression in your breed, or has a list of medical problems to watch for that seems overwhelming. Your vet is trying to help you avoid problems, not telling you that your dog will have any, or all, of the problems listed. Don't be surprised if your vet stumbles a little when asked what the good things about a particular breed are. Those lists are not usually stored in the instant recall portion of your vet's memory!

The Basics of Cancer Therapy

There is a certain look in a pet owner's eyes when they realize that I am just about to say "I think that your pet has cancer." I can almost see a physical reluctance to even hear the word uttered. It is as if it would be better for me to say almost anything else than to say that a dog or cat has cancer. In reality, I don't always view cancer as the worst possible scenario. It is not highly unusual for us to put together a list of differential diagnoses in which we think that a specific type of cancer is the best possible diagnosis in the list. Try to keep this in mind when you are faced with the possibility of cancer.

Based on extrapolations from a few studies, it is likely that over 75% of dogs develop some form of cancer in their lifetime and that cats are not too far behind this figure. Despite this, less than 25% of the cases of cancer that occur in pets are ultimately fatal. Compared to diabetes in both cats and dogs, chronic renal failure in cats or chronic heart failure in dogs, in which the disease is almost always fatal at some point, these statistics look pretty good. The major difference is perspective. We think nothing of advising patients how to manage these other chronic diseases but are much more reluctant to discuss management of a malignant cancer to provide additional comfort and a longer life span.

Some of my clients just stop listening to the rest of what I have to say after I say the word cancer, so I sometimes find myself scheduling a recheck in a day or so to have a second chance to talk to them. This gives the pet owner time to get over the impact of the diagnosis and to realize that there are a lot of questions that they need answers to other than just this diagnosis.

Perhaps the most important first step is to know what kind of cancer is present. There are many different cancers. The best therapy for one type of cancer may not help when another type of cancer is present. The prognosis for some cancers is excellent, even without therapy. The prognosis for other cancers is terrifying, even with aggressive therapy. It is critical to know which type of cancer is present in making any decisions about therapy and prognosis. Some of our clients forgo this information and choose to place their faith in surgical excision of a mass in the hope that it will be curative. There are times when this seems appropriate to me, as well. It is important to remember that prognostic information and the ability to make a plan for future treatment is not possible in most cases if a mass is simply removed and never examined by a pathologist. A decision must be made prior to the surgical procedure or during the procedure to save tissue samples for examination. Tell your vet you want histopathology done on any tumors removed, if you wish to know what they are with the highest degree of certainty.

I have clients who truly do not want to know what type of tumor is present. This is most common when the cost of surgery is already close to the maximum they can spend on their pet and the client knows that there is not going to be an opportunity to pursue further therapy. This decision can be hard for me to accept in some cases but I understand the situation and can deal with it. I have other clients who are so afraid of the diagnosis that they avoid knowing for sure what it is. When I know that these clients might be avoiding treatment that could provide a cure, or could improve the quality of their pet's life, I feel strongly that their decision making is flawed. Listen carefully if your vet strongly suggests having a pathologist examine a tumor after removal.

The first possibility to consider when we include cancer in our list of possible causes of a lump or illness is to find out if it is possible to confirm that diagnosis. It is often possible for us to make a preliminary diagnosis from an aspirate of the lump taken with an ordinary hypodermic needle and syringe. The aspirate is smeared on a microscope slide and examined for signs of cancer or other causes of lumps of bumps. In other cases we can just press the microscope slide on the surface of a tumor and get our sample in this manner. If the fine needle aspirate or impression smear does not provide enough evidence to make a preliminary diagnosis it is usually possible to do a biopsy of the lump for examination by a pathologist, prior to scheduling surgery to remove the entire tumor.

In some cases we strongly suspect cancer but can not find a specific cancer site. This can happen because the tumor is located in a spot where it is hard to find, such as the base of the heart, the brain or some other organ. It can also happen when small tumors are capable of causing major problems. Some tumors produce hormone like substances that can cause dramatic changes in things like calcium levels, even though the tumor is very small. In these cases, we sometimes take the approach of eliminating everything else that could cause the abnormality we find and then fall back on the diagnosis of cancer when nothing else seems likely.

Many times when we find cancer, we find it by accident. There is no indication at all that it is present in the pet's behavior, habits or physical state that indicate a problem is present. It is not unusual at all for complete blood counts and serum chemistry tests to be completely normal in a patient who has cancer. People tend to think that their pet should be very ill in general when cancer is present but it is important to remember that this is often not the case. While the cancer may eventually cause severe problems, including death, it may cause only minor problems for a very long time.

After diagnosing cancer and getting a specific idea of the type of cancer present, the next step is to figure out what the diagnosis means. There are many specific types of cancer. Some of them are, like lipomas, are almost always benign. These cancers might grow where they are, sometimes even to very large sizes. They don't spread to other areas of the body and they don't aggressively invade surrounding tissues, though. This type of cancer has an excellent prognosis even if nothing else is done. In fact, the risk of surgical removal of a lipoma is probably higher than the risk of leaving the lipoma alone. Once in a while we have a client who positively insists on having a lipoma removed because they are just unable to accept living with any type of cancer. This is probably an example of poor risk assessment, though. Why take a 1 in 500 chance of losing a pet to an anesthetic crisis for a tumor with a 1 in a 2000 chance of being malignant? On the other hand, if the tumor is malignant but can be surgically removed with good tissue margins, the risk of anesthesia becomes a minor concern, since the odds are much different. While anesthesia might cause death in 1 in 500 dogs, mast cell tumors will eventually kill 7 out of 10, or more, of dogs who have them. Careful surgical removal of Grade 1 and Grade 2 mast cell tumors can completely reverse these odds, providing a 7 out of 10 long term survival rate. Knowing which tumor is present allows you to think about the risks of the tumor, the risks of the possible treatments and to assess these risks like you would any other disease. By doing this, it is often possible to gain enough information to make decision making easy rather than difficult. So the first two rules are:

1) Be sure that cancer is actually present

2) Make a plan based on the exact type of cancer that is present

and its known response to various types of therapy.

It is here that I need to skip from specifics back to general information. It is important at this point to understand that even if it is necessary to consider chemotherapy, radiation therapy, radical surgery the main goal for you, as the pet owner, should be to provide the best possible patient support, regardless of the other choices made. Next month I will try to provide specific treatment information for some of the most common types of cancer. This month, I want to try to reassure you that it is possible to consider all of the options for cancer therapy without feeling that you are completely sacrificing quality of life or patient comfort. Hopefully this will help you play a big role in your pet's response to aggressive cancer treatments and that it is possible to choose these options, when they seem appropriate to you, without having to feel so guilty about putting your pet through a difficult therapy.

For the most part, the rest of this discussion will be about malignant cancers for which treatment is available but may not provide a cure. The most appropriate way to start this part of the discussion is probably to ask why it is reasonable to choose to provide expensive and sometimes uncomfortable therapy that is likely to increase a pet's expected lifespan by months rather than years. For most pet owners, scientific reasons to treat cancer, such as the hope of finding a future cure based on responses to current treatment protocols, is not very meaningful when it comes to an individual pet's care. However, we can only learn to improve cancer therapy by participating in the process, so it is something to consider. For most pet owners who elect to treat for cancer the reasoning is more personal. I believe that the clients who can empathize with their pets make the best treatment decisions. I truly believe that it is best to ask yourself how you would like to be treated if you were the pet, facing the treatment and facing the possibility of living with the cancer. Would you be willing to undergo the proposed therapy, keeping in mind the potential side effects, for the average amount of benefit the therapy can provide? To take this just a little further, with your best evaluation of your pet's personality, would your pet make the decision to undergo therapy knowing the potential problems and probability for a successful cure or at least control of pain and discomfort? If you feel the answer is yes, then treatment is justified.

Whether you decide that you will attempt treatment for cancer or would prefer not to, there are still more decisions to be made. As you evaluate how to best control the side effects of treatment or to provide patient support if treatment is not an option, you start to run into a whole new set of rules for cancer therapy. The single most important rule is that patients should not suffer in any way that is preventable.

Surgery is the mainstay of cancer therapy in many veterinary practices. Despite this, many veterinary surgeons are not very good at cancer surgery. There is a strong tendency among general veterinary surgeons and even some surgical specialists to forget to properly plan cancer surgeries to maximize the benefits. It is best, whenever possible, to know the type of tumor that is present prior to planning the method of removing it. This means that it is usually better to have some sort of biopsy results prior to the surgery in which an attempt is made to totally remove a tumor. These can be the simpler techniques, such as fine needle aspirates or impression smears that can be done in the veterinary office or they can be surgical biopsy samples that have been submitted for review by a pathologist. If there is any suspicion that a potentially malignant tumor is present it is best to have a pathologist's opinion when possible. If the pathologist confirms that the tumor is malignant and provides an opinion of tumor grade or aggressiveness that is strongly suggestive of a tendency to metastasize, it is a good idea to try to be sure the tumor hasn't already spread prior to surgery. Chest and abdominal X-rays may be necessary, examination of surrounding lymph nodes may be helpful, a careful assessment of the skin for evidence of tumor spread can be helpful and for some tumors there are other specific tests that can indicate tumor spread. If the tumor has spread it may be necessary to consider options other than surgery.

If the tumor has not obviously spread, but is highly likely to, removing a wide margin of tissue in all directions is critical. The part of this surgical option that most veterinarians are unwilling to face is the need to remove two centimeters of tissue UNDER the tumor. The reason that this is often the complicating factor is that removing an inch of tissue under a tumor often means removing underlying bone, deep muscles, nerves or other tissue that has a useful purpose and is difficult to remove without complications. This is why it is often best when dealing with especially aggressive tumors, such as vaccine associated sarcomas in cats or high grade mast cell tumors in dogs to have an oncologic surgeon perform the surgery. Surgeons who remove malignant tumors on a regular basis are much more likely to remove the necessary tissue and just deal with the complications than a general practice veterinarian. They are also often better equipped to deal with complications such as the need to remove underlying bone than a general practitioner is.

The most difficult decision to make for many people is whether to amputate a leg in order to remove sufficient tissue to prevent spread of a tumor. This is always a hard decision to make but there are some factors to consider. Dogs and cats seem to function better after rear leg amputations than after front leg amputations. Small to medium sized dogs and most cats tolerate front leg amputations pretty well, too. I am almost always surprised at how well cats do with rear leg amputations. We have five to ten cats in our practice with rear leg amputations and it is often hard to see any problem at all in these patients as the result of the amputation. If there is preexisting arthritis in several limbs, it is more likely that problems will occur as the result of an amputation. Obesity is another complicating factor. All in all, though, most pets do well with amputations, even very large dogs. This is another area in which a pet's attitude towards a problem is often different than a person's. Most dogs and cats just seem to accept the situation and move on. While it is a little harder to put yourself in the position of your pet in trying to decide if an amputation is appropriate, I do think a general assessment of your pet's past responses to difficulties with injury or temporary disabilities can help guide your decision making. If your pet was willing to walk on three legs because of a cruciate ligament injury or other temporary problem without complaining, he or she will probably do so after an amputation, too.

Older dogs and cats generally tolerate anesthesia and heal after surgical procedures just as well as younger dogs and cats. There may be preexisting problems that require identification and management during the anesthesia and surgery, though. For cats the most common complication affecting surgery is kidney failure. It is important in older cats to check the status of the kidneys prior to surgery and to provide adequate hydration intravenously or subcutaneously during surgery and during the recovery period if there is any evidence of preexisting kidney disease. In dogs there is a stronger tendency for chronic heart failure to be a problem and this can be complicated by chemotherapy or by interactions with anesthesia and some of the pain relief medications. It is important in both dogs and cats to be sure that the surgeon is aware of all medications, including over the counter medications, herbs, homeopathic preparations and prescription medications such as corticosteroids or phenobarbital that are being used for conditions other than the cancer.

Radiation therapy causes side effects. Most people have an image of these effects that lies somewhere between memories of photos of victims of nuclear bomb attacks and memories of seeing a relative or friend with hair loss or signs of skin irritation similar to sunburn. Radiation therapy is available for veterinary patients in many areas of the country but it hard to obtain in others. Several of our patients have had radiation therapy. The first time a client opted for this therapy I was expecting to have to provide a great deal of supportive care after the therapy. We did have to provide a small amount of aftercare. I suspect that the veterinarians administering the radiation therapy dealt with more complications than we did. I believe that they work hard at this and it is easy for pet owners to overlook these complications since many pets are hospitalized during the therapy but it is best to ask about possible complications and to find out how they will be treated. The biggest long term problem we have had after several patients have been treated has been an oronasal fistula (hole between the oral cavity and nasal passages) that developed in a patient treated for squamous cell carcinoma. It is sometimes necessary to prevent pets from traumatizing damaged skin, so it may be necessary to accept the use of an Elizabethan collar or other means of limiting self-trauma for several weeks. Hair loss does occur but for pets I truly think this is a minor complication since pets don't think about it the same way humans do. Radiation therapy works extremely well for some tumors and provides only pain relief or palliative therapy in for other tumors. The potential for side effects varies according to the type of tumor and the intended effects. A realistic assessment of the benefits of this therapy would probably result in more use, rather than less use, of radiation therapy in pets. It is costly and the access is limited but if it can be an option worth considering.

Chemotherapy scares most people more than surgery or radiation therapy. Almost everyone knows of someone who had terrible reactions to chemotherapy and did not experience enough benefit to make it seem worthwhile. This creates a resistance to considering chemotherapy that is not always justified. There are about fifteen commonly used chemotherapeutic agents. In general, toxicities associated with these medications involve the digestive tract and bone marrow. Specific drugs may have different effects. Doxorubicin causes heart muscle damage over time, for example. For many clients the most obvious sign of toxicity is going to be vomiting or diarrhea. It is often possible to control vomiting pretty well with additional medications. For veterinarians the effect that usually causes the most concern is bone marrow suppression leading to very low white blood cell counts. When this happens it is sometimes necessary to delay further therapy or to hospitalize and monitor a patient if the low white blood cell counts are accompanied by fever or other signs of an infection. Chemotherapy requires a much higher level of commitment on the part of the pet owner than other forms of therapy for cancer, due to the need to carefully handle contaminated stool and vomitus, the need to make repeated trips to the oncologist for therapy and the need to be vigilant about monitoring the pet's overall health during the time of chemotherapy. Despite this, most of our clients who pursue chemotherapy for their pets are glad they made the decision even after their pet eventually does succumb to the cancer. I think that chemotherapy is a difficult choice but that it should not be ruled out instantly. Take the time to find out what chemotherapeutic agents are used for the cancer, the duration of therapy that is necessary, the degree of commitment it will require and the expected outcome, before making a decision.

Cancer patients have many needs that arise as a result of their disease, other than the need to kill the cancer. One of the most important needs is pain control. It is very important not to limit your options for controlling discomfort or pain for your pet. Many veterinarians are reluctant to provide narcotics or to write prescriptions for them. There is some risk that narcotics will be diverted to use by drug abusers but this does not justify withholding a necessary medication for a pet's well being. The fear that a pet will become addicted to narcotics is much less of a concern because the veterinarian and pet owner control the dosage and availability of the medications entirely, a situation that doesn't exist in humans who might become addicted to medications. It can be very difficult to tell if a pet is in pain. It is almost always better to assume that a situation that can cause pain in a human is causing pain in a pet and to treat accordingly. Do not passively accept a veterinarian's reluctance to adequately control pain in your pet. If necessary, obtaining adequate pain control is sufficient reason to change veterinarians.

We usually try to control pain first with non-steroidal analgesics. We have the best success in cancer patients using carprofen (Rimadyl Rx) and ketoprofen (Ketofen Rx) but etdolac (Etogesic Rx, Lodine Rx) and piroxicam (Feldene Rx) are also useful. Piroxicam is especially useful in bladder tumors and can be helpful with tumors in the nasal passages, as well. If these medications cause gastrointestinal problems it is possible to continue their use in some patients by adding misoprostal (Cytotec Rx) as a GI protectant.

There are benefits in pets to the use of tricyclic antidepressants, such as amitriptyline (Elavil Rx) or imipramine (Tofranil Rx) to supplement pain relief. These medications seem to have both an additional analgesic effect and the benefit of depression control. Local anesthetic agents can be used for pain at surgical sites or from complications of radiation or photodynamic therapy. Sometimes the combination of a NSAID and one of the tricyclic antidepressants will provide sufficient pain control that neither can provide alone.

Often, it is not possible to achieve adequate pain control without using narcotic pain relievers. There are several effective opioid pain relievers. Codeine is available in combination with acetaminophen and is reasonably safe to use in dogs. This combination should not be used in cats. Morphine can be used in both dogs and cats, although it must be used with a little more caution in cats due to the potential to cause extreme excitement in this species. Sustained release morphine (MS Contin Rx) can be used in dogs but is not advisable for cats because the tablets can not be broken and so accurate dosing is not possible in cats and small dogs. Duragesic (Rx) patches contain fentanyl, an opioid pain reliever which is released slowly over the course of three to five days. Pets should not be allowed to chew on or swallow the patch, so the use of these patches must be monitored closely. Swallowing a patch could lead to absorption of the entire dosage at one time, which could lead to an overdose. Veterinarians are obligated to provide adequate pain relief for their patients. If opioid medications are the only way to provide effective pain relief then they should be used for that purpose.

It is possible to keep most pets from vomiting during chemotherapy by using odansetron (Zofran Rx) or doasetron (Anzemet Rx), although these are medications that must be given by intravenous injection. If your pet is reacting to the chemotherapeutic medications by vomiting, report this to your vet and ask about this type of therapy if the vomiting is severe. Many general practitioners are reluctant to stock these drugs due to cost but I think that specialty practices dealing with many cancer patients often do keep these medications on hand. Pets on chemotherapy who have diarrhea often respond well to antibiotic therapy or the use of motility modifiers like loperamide (Immodium AD tm).

When we know that cancer is present, it is necessary to consider making dietary changes in order to compensate for the effects of cancer. The major consideration for most patients is providing adequate caloric intake to offset the cancer's use of energy. Many older pets are on diets designed to reduce calories, or fat in the diet, since older pets are less active. These diets are not good choices for a patient with malignant cancers and some forms of benign cancer, however.

Cancers utilize energy from carbohydrates better than other forms of energy. For this reason, it can be helpful if diets for cancer patients contain lower amounts of carbohydrate. Proteins can be used by tumors for energy purposes but there is often additional need for protein in pets with cancer. For this reason, using a high quality protein in the diet in moderate amounts may be a good compromise between the needs of the patient and the need to limit the cancer's energy sources. Fat has the most stored energy and is the most difficult source of energy for tumors to utilize, so a diet that uses fat to provide the majority of the calories should benefit the cancer patient. The total energy expenditure in cancer patients is often normal, or even less than normal, while they continue to lose weight. By manipulating the energy intake to favor the patient over the cancer it is possible to help prevent the weight loss and it's effects on the pet.

When pets refuse to eat during therapy for cancer consideration should be given to using implanted feeding tubes. Many people have an extreme aversion to this form of feeding, based primarily on the human experience in which patients are kept alive in vegetative states through the use of feeding tubes and supportive care. This does not happen in pets due to the right of pet owners to request euthanasia when it is deemed necessary. The most common use of feeding tubes in pets is short term use of nasogastric or esophageal feeding tubes to allow a pet to get through a rough period, after which tube feeding is not necessary. In pets, providing adequate nutrition can be the difference between surviving a short term crisis and dying from it, so if your vet suggests this procedure it is worth considering.

There are a huge number of nutritional supplements which are promoted as having beneficial effects in cancer patients. Of these, the two that have the best track record in controlled veterinary studies are Vitamin E and omega-n3 fatty acid supplements, such as marine fish oil (3V Capsules tm). If you use supplements of any kind please let the oncologist know that you are doing so. Some supplements interact with chemotherapeutic agents or medications that may be used for cancer patients and it may be necessary to compensate for this effect.

Try not to forget that many cancers can actually be cured, most commonly through proper surgical removal but sometimes with chemotherapy or radiation therapy. Other cancers may ultimately be fatal but the course of the disease can be managed in such a way that the patient can be comfortable for some time prior to the onset of severe complications. Don't forget that cancer care is a joint effort between you and your vet. You are at least as important as your vet, ultimately, by providing good nursing care and managing pain and nutritional support. Try to empathize with your pet and provide the kind of care you would hope to receive if you had the same problem. If you do this, you will provide care you can live with, too.

Proheart 6 (tm)

ProHeart 6 (tm), an injectable form of heartworm prevention medication, is now available. This medication is the first time-release product produced for heartworm prevention and a single injection will protect dogs for 6 months. In Australia, a slightly different version, ProHeart (tm) 12, is available and works for 12 months. ProHeart has been approved for heartworm prevention in Australia for most of this year and so far, the Australian veterinarians seem to be happy with the product. In the U.S. Proheart was approved for use in June and should be available at your veterinarians at this time. The injection works due to a "microsphere" technology that slowly releases the active ingredient, moxidectin, over time. In the United States this product is approved for dogs over six months of age. At this time the product is not approved for cats.

For dogs who do not like the monthly heartworm preventative medications or in cases in which it may be difficult to give the monthly medications, such as an extended vacation, this product should be very useful. It is priced to be competitive with the monthly prevention medications and is likely to be less expensive for many dogs, since it can be dosed more precisely, which should save on medication costs for dogs at the lower end of the dosage range for each of the monthly preventative sizes.

Thanks for Your Support!

If you send us e-mail, remember that Michal Justis answers the e-mail at vetinfo@vetinfo.com. E-mail sent to mervet@inna.net is answered by Dr. Michael Richards.

The VetInfo Digest is published by:

TierCom, Inc.

P.O. Box 476

Cobbs Creek, VA 23035.

The opinions expressed in this newsletter are those of Michael Richards, DVM., author.

Copyright 2001, TierCom, Inc.