Dispelling the myths of veterinary cancer and its treatment (Proceedings)

Often, the primary clinician may be the veterinarian making a diagnosis of cancer in a pet and performing the initial client education regarding their pet's disease. Critically important, life-or death decisions regarding euthanasia, treatment, choice to pursue referral, etc. may be made based on information that the owner gets from their primary veterinarian. There is still a great stigma attached to a diagnosis of cancer, and it is natural for owners of pets with cancer to anthropomorphize and equate cancer treatment in animals with experiences they may have had with treatment of themselves, their friends or family members. Being able to succinctly address these concerns and "dispel" some of the myths that owners may have is critical component of cancer management in the primary care setting. There are, additionally some myths or misconceptions that veterinarians and staff cling to that may alter their approach to the cancer patient or the information they impart.

Is cancer really a problem in pets? Unfortunately, yes. It is the leading "natural" cause of death in dogs, and the 2nd or 3rd most common cause of death in cats. Up to 50% of dogs and 30-35% of cats will be affected by some type of tumor in their lifetime.

Why does is seem like there so much more cancer in pets these days? Better pet health care = longer life. We are getting so good at managing other husbandry-related conditions in dogs (nutrition, infectious/parasitic disease, keeping pets indoors and on leashes) that they are now living long enough to develop more geriatric conditions such as heart disease, kidney disease, endocrine disease, and cancer.

Did something in the environment play a role in my pet's cancer? Was I feeding the wrong food? There have been some weak associations proposed between certain types of cancer and environmental influences (canine lymphoma and certain herbicides or living in urban environments, canine mesothelioma and asbestos, feline gastrointestinal lymphoma and environmental tobacco smoke), but in the vast majority of cases no such association can be made. Thus, for the most part, food additives, lawn chemicals, pesticides, cosmic rays, etc. do not seem to significantly increase an animal's risk of cancer.

Why treat animals with cancer? Because we can! We treat many animals with chronic disease that are never cured (Diabetes, other endocrine diseases, heart disease), and cancer is another chronic disease. Furthermore, cancer is a disease that we can sometimes cure! Even in cases where cure is unlikely, there are many cancers where we can extend an excellent quality of life with treatment.

Do we have to do XXX for this lump now? Can't we just wait and see what happens? Owners may use this phrase regarding initial diagnostics (let's wait and see if it grows), additional surgery or other treatments to prevent local recurrence after incomplete excision (let's wait and see if it grows BACK), or therapy to delay or prevent metastasis (let's wait and see if it spreads). Let's wait and see if it grows: In general, delay in achieving a diagnosis only serves to increase the difficulty of surgery and, potentially, the likelihood of metastasis. Larger tumor size is statistically associated with worse outcome for several important veterinary cancers, including canine and feline mammary carcinoma and canine melanoma. The lump they are dealing with may very well be nothing, but if it is a tumor, the time to find that out is sooner rather than later. Let's wait and see if it grows back: Locally recurrent tumors are statistically associated with a worse prognosis in certain diseases such as canine mast cell tumor and oral melanoma, and suspected of being worse in others such as feline vaccine-associated sarcoma. For this reason, the time to get aggressive is the very first time the tumor occurs. Let's wait and see if it spreads: In general, treatment of gross metastatic disease is palliative at best. Asking drugs to kill a big bulky tumor is asking a lot, but asking those same drugs to have an effect against microscopic tumor cells in the lung or lymph node may be a much more reasonable goal. For example, the approximate median survival time for dogs with osteosarcoma undergoing amputation, but not receiving chemotherapy until the time of metastasis, is approximately 4 months whereas dogs receiving chemotherapy for microscopic metastasis immediately after surgery is approximately 12 months.

Doesn't performing a fine needle aspirate/biopsy make the tumor "angry" and increase the risk of spread? NO. Getting from the primary tumor into the blood stream is only one of many steps in the "metastatic decathlon". There are probably many circulating tumor cells in the body all the time, but it is only those rare tumor cells with the complete genetic program that allow them to survive at a distant site and successfully metastasize. Exceptions to this rule are: (1) Some mast cell tumors may become "inflamed" following a fine needle aspirate due to degranulation and histamine release, although this in no way hastens metastasis. This is rarely serious and can be treated or prevented with an H1 blocker; (2) Transabdominal needle aspiration/needle core biopsy of splenic and bladder masses is contraindicated, due to the risk of local dissemination in the abdomen and/or seeding of the biopsy tract. (3) It is important to plan needle aspirates and biopsies of cutaneous/subcutaneous masses so that the biopsy tract can be incorporated into the definitive surgical excision to prevent recurrence along the tract.

Why don't we just take the tumor off? Why do we need to do a FNA/biopsy first? Obtaining a diagnosis prior to surgery helps to plan the surgical approach and lets the clinician know whether additional tests are indicated prior to surgery. This helps avoid situations like "Why didn't you take X-rays before surgery?" and "Why should I have to pay for a second surgery if you 'didn't get it all' the first time?". If excisional biopsy it to be used to obtain a diagnosis, it is wise to forewarn the owner that this test is only being used to obtain a diagnosis, and that additional diagnostics or treatment might be necessary, based on the results.

Why should I pay for histopathology? Why don't you just take it off and throw it away? If it's worth removing, it's worth submitting. Many practices are incorporating the histopathology fee into the surgery package, so it is not optional. See "just wait and see" above for problems with the "we'll submit it for histopathology if it recurs" approach. Similarly, it is important to avoid submission of parts of excised tissue or a "representative section" of an excised mass. This cuts the information gleaned from the pathology report in half, as surgical margins cannot be interpreted. If a mass is too large to be sent in, then the pathologist can be consulted for directions on which sections to send in and how to label them to insure that margins are evaluable.

My Great Aunt Harriet had chemo, and she felt miserable all the time - I'd never do that to my pet! The drugs we use to treat cancer in animals are the same drugs that humans get, but we give considerably lower doses and don't give as many at the same time to minimize the risk of adverse effects. With most chemotherapy protocols in common use, less than ⅓ of patients experience unpleasant side effects, and 5% or less experience a severe side effect. The rare adverse effect necessitating hospitalization can usually be fixed in 24-72 hours. The likelihood of a chemotherapy-related fatality is less than 1 in 200. Should unpleasant side effects occur, doses can be reduced, drugs can be substituted, or additional medications dispensed to minimize the likelihood of further adverse effects. These changes are effective 90% of the time.

OK, suppose my dog is the unfortunate one that has a side effect? What kind of side effects are we likely to see? This varies by agent, but in general the most common side effect is something related to the gastrointestinal tract – perhaps a few days of decreased appetite, mild nausea or vomiting, or loose stool. By way of comparison, it's usually not too different from what you might see if a dog got into the garbage. They might need to eat some bland food for a few days or take some antinausea or anti-diarrhea pills at home. Usually this doesn't persist for more than 3-5 days. Some dogs have the potential to develop neutropenia. We check this quite frequently, and most of the time it is not low enough to be dangerous. In some cases, a patient might need some oral antibiotics at home, or a treatment might need to be delayed for a few days. If a patient develops a serious side effect, it is usually either REALLY BAD vomiting/diarrhea (can't keep anything down, getting weak/dehydrated) or dangerous neutropenia that renders them susceptible to a bacterial infection.

I don't want Fluffy to go bald! It is true that certain dog breeds (the so-called non-shedding breeds) can lose some hair from chemotherapy. It is rarely complete. Most other breeds experience little or no hair loss, although the owners will probably find more hair around the house and long-haired breeds have the potential for excessive matting. Hair loss from chemotherapy is non-itchy and nonpainful – it is a purely cosmetic change. Hair that is lost will typically begin to regrow approximately 1 month following the completion of therapy. Cats may lose whiskers and the long, stiff "guard hairs" of their coat.

I don't want Spike's last weeks / months / years to be in and out of the hospital, like they were with Uncle Mac when he had cancer. Almost all veterinary chemotherapy treatments are done in an outpatient setting, and the majority involve quick injections rather than prolonged infusions (there are exceptions to this however). Many protocols involve a series of treatments, followed by a period of careful observation. Continuous, indefinite chemotherapy is not the norm.

I don't want my family / guests / house / other pets to be contaminated. Urine and feces pose a minimal risk to owners -- few drugs are excreted for longer than 48-72 hours. Common sense (i.e. wear gloves when handling urine or feces) is usually sufficient. Accidents in the house during this period should be cleaned using a dilute bleach solution and the excreta flushed down the toilet. Normal daily interactions (grooming, playing, petting, handling food and water bowls) pose no real risk. It is important that owners are instructed to wear gloves when handling oral medications, and that pills not be crushed or split nor capsules opened.

But what about Muffy's age? Isn't she too old for treatment? AGE IS NOT A DISEASE! Most of the patients we treat with cancer are older pets. Statistics regarding effectiveness, survival and tolerability of cancer therapy are usually generated in a population of older patients. Far more important than chronological age are general health (e.g. cardiovascular, renal) and performance status (e.g. how are they feeling?).

So what are our choices? We either do chemo or put him to sleep? Chemotherapy (and cancer therapy in general) is generally not an "all-or-nothing" proposition. For may tumor types, a spectrum of treatment options may be available depending on owner availability, finances, willingness to tolerate side effects, etc. For example, there are various treatments for canine lymphoma from which an owner can choose, including prednisone alone, prednisone plus single-agent doxorubicin, cyclophosphamide/vincristine/prednisone, or a multi-agent injectable protocol such as the UW-Madison protocol. All have different costs, risks of side effects and numbers of trips required and varying degrees of efficacy. For appendicular osteosarcoma, amputation and platinum-based chemotherapy may be the optimal treatment, but other options could include palliative radiation therapy or amputation plus doxorubicin.

What about radiation therapy for my pet's tumor? Radiation therapy can be very useful for certain neoplasms. Since it is a local treatment, it is most often used to treat local disease, e.g. tumors with a high likelihood of aggressive local infiltration but a low risk of metastasis. Common examples include postoperative treatment of incompletely excised low-or intermediate-grade mast cell tumors, soft-tissue sarcomas including vaccine-associated sarcoma in cats, oral tumors such as fibrosarcoma, squamous cell carcinoma and the dental tumors, and perianal tumors. It can be used prior to surgery in certain cases to render an inoperable tumor more amenable to surgery. It can also be used as the primary therapy for certain tumors such as nasal tumors, CNS tumors and acanthomatous epulis. Finally, it can be used to provide palliation in some highly metastatic tumors such as osteosarcoma and malignant melanoma. The majority of "definitive" or "full-course" radiation therapy protocols in common use involve a series of 10 to 25 treatments delivered either Monday through Friday or three days per week for several weeks. Although there is no reason why these treatments cannot be delivered on an outpatient basis, many animals will spend some of the time in the hospital for practical, travel-related reasons. Most "palliative" or "coarsely fractionated" radiation therapy protocols will involve 1 to 6 weekly treatments on an outpatient basis.

But won't Charlie be horribly sick from radiation? Radiation therapy is a local form of therapy – the radiation is only delivered to the site of the disease. Thus, systemic side effects (nausea, fatigue, bone marrow suppression) generally do not occur. However, each treatment does require very brief anesthesia or heavy sedation to insure that the radiation is delivered accurately. In theory there could be systemic adverse effects as a result of this, but they are very rare in the patient with normal cardiopulmonary, renal and hepatic function.

What about the horrible radiation burns? It's true that animals receiving radiation therapy can develop varying degrees of a sunburn-like reaction at the site where the radiation is delivered. These can range from mild erythema and pruritus to moist, oozing or ulcerated skin. Many animals will need to wear an Elizabethan collar to prevent self-trauma and/or receive oral antibiotics or analgesics during this period. These effects typically do not start until the second or third week of treatment and are resolved within 2-4 weeks after the completion of radiation therapy. The animal can be left with an area of irradiated skin that is permanently hairless, the hair may grow back only partially, and may turn white within the radiation field. Chronic, long-term side effects are rare, with the exception of the eyes in animals receiving radiation therapy for nasal, oral or brain tumors.

Will Tuffy be radioactive when he comes home? The standard form of radiation therapy in animals is external beam, i.e. radiation is shone down from an external source, practically not that different from a diagnostic X-ray except using higher energy particles. Animals undergoing radiation therapy pose no health risk to their owners.

What can we give just to make Rover feel better for whatever time he has left? We are often called upon to provide palliative care for our cancer patients. Perhaps the most common clinical signs we are asked to address are pain and poor appetite. Often a reflexive action is to reach for corticosteroids to address these signs. Corticosteroids can be very useful for certain type of tumor, where they can have a direct antitumor effect (lymphoma/leukemias, mast cell tumor, myeloma) or where specific clinical signs can be addressed (e.g. hypoglycemia and insulinoma, hypercalcemia, neurologic signs from CNS tumors). However, corticosteroids are not useful, and could be potentially harmful as a result of their adverse effects and negative impact on tumor progression (immunosuppression). For these conditions, alternative analgesics (NSAIDs, opiates) and alternative appetite stimulants (megestrol acetate, cyproheptadine, antiemetics) can be considered first, saving corticosteroids as a "last resort".

References

Withrow SJ. Why worry about cancer in pets? In Withrow SJ, MacEwen EG (eds): Small Animal Clinical Oncology, 3rd Ed. Philadelphia: Saunders, 2001. pp. 1-3.

Harvey A, Butler C, Lagoni L, Durrance D, Withrow SJ. A bond-centered practice approach to diagnosis, treatment and euthanasia. In Withrow SJ, MacEwen EG (eds): Small Animal Clinical Oncology, 3rd Ed. Philadelphia: Saunders, 2001. pp. 672-682.

Chun R, Garrett L, MacEwen EG. Cancer chemotherapy. In Withrow SJ, MacEwen EG (eds): Small Animal Clinical Oncology, 3rd Ed. Philadelphia: Saunders, 2001. pp. 92-118.

Moore AS. Radiation therapy for the treatment of tumours in small companion animals. Vet J 2002;164(3):176-87.

Thrall DE. Biologic basis of radiation therapy. Vet Clin North Am Small Anim Pract 1997;27(1):21-3.

Lester P, Gaynor JS. Management of cancer pain. Vet Clin North Am Small Anim Pract 2000;30(4):951-66.