This paper is written in hopes to give feline caregivers general knowledge of cancer as well as an understanding of the diagnostic and therapeutic options that could potentially be offered to their feline companion. Cancer is a very complex disease including many different types, with each type offering a multitude of therapeutic options. This article should be used as a guide in combination with a general veterinary practitioner and veterinary oncologist, to assist a caregiver in asking appropriate questions and making an informed decision that will ultimately offer their feline companion the best quality of life and comfort.
Cancer is generally believed to arise from changes in a single cell, giving rise to uncontrolled, unorganized, and purposeless growth of a single cell line. Normal cellular division creates a constant flow of injured genes that are regularly corrected by innate repair mechanisms present in normal cellular function. By escaping these regulatory restraint mechanisms these "renegade" cells continue to grow and divide using the same mechanisms as normal cells making their divisions uninhibited, reckless, and a foundation for cancer. Cancer is generally classified and named based on the cell of origin. Although the term cancer is defined as one encompassing disease, there are over one hundred different types of cells in the body, each having the potential of giving rise to cancer. Since cell types serve different functions within the body, this allows for unique variations, characteristics, and behavior when inflicted with cancer. Different types of cancer have an affiliation for different systems within the body. For instance some may come in the form of a tumor within the skin, whereas others may target a specific organ. Cancer may also be present in a diffuse nature without the existence of any focal lesion and may be attacking cells within the blood or lymphatics and associated lymph nodes.
Diagnosing cancer in a geriatric feline patient can be challenging due to initial signs being subtle and often camouflaged by general signs of aging, such as "slowing down", lethargy, reduced appetite, dental disease, changes in weight, muscle loss, and abdominal distension. Detecting cancer in the earliest possible stage offers the geriatric feline the best chance of survival from cancer.
In the presence of a tumor or lesion a fine-needle aspirate (FNA) should be performed to help identify the tumor. FNA offer the benefit of possibly identifying the presence of cancer both inexpensively and non-invasively by simply placing a needle into the tumor and pulling back a sample of cells. Although this procedure can be invaluable it also has the potential to be inconclusive and offers little information on the overall behavior of the cancer due to its limited sample size. To properly identify the behavior of the cancer a surgical biopsy sample will often need to be performed. FNA of regional lymph nodes adjacent to a tumor is also imperative in evaluating the invasiveness of the cancer.
With or without the presence of a tumor or lesion a complete-blood-count, biochemistry profile, assessment of thyroid function, urinalysis and determination of Feline leukemia/Feline immunodeficiency virus status should always be performed to evaluate the feline's overall health as well as to help classify and prognosticate the cancer.
Abdominal and thoracic radiographs should be performed to identify the presence of tumors, and evaluate the invasiveness of the feline's cancer. The thorax is one of the most common places for cancer to metastasize, and its presence is an important prognostic indicator. Although radiographs serve as a good scan of the animal, many small lesions can be missed, therefore more specialized modalities are available such as ultrasound, magnetic resonance imaging and computed tomography to pinpoint lesions not detected by radiography.
When a feline is diagnosed with cancer a prognosis will often be given in the form of a percentage. This percentage is based on statistical analysis of other cats diagnosed with the same or similar cancer and their average response to therapy. These statistics often do not take into consideration the age of the cat at diagnosis or any concurrent disease states. It is important to understand that this figure is not a guarantee but an educated guess and that some cats may respond significantly less than or more than the predicted outcome.
When treating cancer in the geriatric feline it is important to first approach treatment and care with the understanding that "age is a condition not a disease". Treating cancer in geriatric felines is more complex often due to concurrent ailments or compromise to other organ systems, posing limitations in both the drugs administered as well as anesthetic risks. Although daunting, it is important to understand that this is not an impossible task and can be very rewarding and well worth the effort. Each patient should be approached on an individual basis to provide the most optimum treatment protocol for his or her health and well-being. There are numerous treatment modalities that can be tailored and combined to reduce toxic levels and offer ultimate comfort to your companion.
Chemotherapy: Chemotherapy acts on rapidly dividing cell populations by interfering with DNA synthesis or cell division. In an ideal situation chemotherapeutic drugs would only target the cancer cells without causing any harm to normal cells. However, unfortunately and at least at this time, such a drug is not in existence. Chemotherapy is toxic and kills by percentage. Meaning the goal of chemotherapy is to consistently kill a high enough percentage of the diseased cells to suppress the cancer's progression, while not jeopardizing the overall health of the patient. In general, chemotherapy is often associated with preconceived notions from people's own experience with human chemotherapeutic modalities. Research has shown that although side effects do occur with chemotherapeutic drug use in veterinary patients, animals tend to have decreased effects in regards to nausea and weakness. In people, higher doses are used resulting in a much greater risk of side effects as doctors are hoping for a very long-term duration of remission. For example, it seems reasonable to risk making a person extremely ill for six months to gain twenty years of life. However, in the case of treating a geriatric feline, whose average life duration is fifteen to seventeen years, six months with the risk of severe side effects isn't a practical option. Instead it is more reasonable to use a lower dosage and strive for four to five cancer-free years. Felines on chemotherapy may experience some hair loss, most commonly with the loss of their whiskers. The hair will usually grow back, however the hair may be a different color or texture.
There are a large variety of chemotherapeutic agents, each containing their own unique properties of killing cells at different stages. For this reason, it is common to use a combination of drugs, referred to as a "protocol". With the guidance of a veterinary oncologist all options of treatment can be presented along with the prognosis they offer. Once again concurrent disease, such as renal disease, liver disease, hyperthyroidism, heart disease, just to name a few, could eliminate some specific drugs from use due to their direct effects on organs or routes of metabolism and excretion. Chemotherapeutic drugs come with the risk of side effects, including increased urination and thirst, nausea, vomiting, diarrhea, anorexia, bone marrow suppression, heart disease, renal disease, and blindness. However, each drug is associated with its own variation of these side effects and with the guidance of an experienced oncologist and the individual health of each patient the benefits and risks can be weighed and options to avoid and diminish these risks can be discussed. For instance a drug may be initialized at a decreased dose with the possibility of being slowly increased to allow for early detection and interference of toxic events.
Chemotherapeutic drugs can also be offered with different routes of administration. The majority of regimens require repeated intravenous administration, requiring the placement of an intravenous catheter to prevent the drug from exiting the vein and causing necrosis and sloughing of surrounding tissue. Some of these drugs must be given slowly over a couple of hours along with fluid therapy, requiring hospitalization for the day. For some felines intravenous therapy is a realistic option, whereas for others the stress of repeated veterinary visits and the placement of an intravenous catheter is overwhelming and could greatly affect the animal's overall quality of life. It is therefore important to understand that there are chemotherapy protocols that reduce the number of necessary administrations, could simply be administered as an injection under the skin, or even orally from home, eliminating veterinary intrusion altogether. Most oral chemotherapeutics are coated to protect any adverse effects to the person administering the medication in addition to the use of latex gloves for optimum protection. Oral chemotherapeutics are also one of the more inexpensive options available in comparison to other chemotherapeutics.
Feline alimentary lymphoma, cancer of the gastrointestinal tract, is one of the most responsive types of cancer that can be treated with multi-agent chemotherapy. Alimentary lymphoma is currently the most common cancer seen in geriatric cats. The extent of the cancer will determine the treatment, however in cases where there is more than one lesion within the gastrointestinal tract and surgical removal is not an option, chemotherapy offers the best prognosis, estimating to achieve remission in approximately 87% percent of cats and offer a survival time of 49-210 days.
Surgery: Surgical removal remains the best option in providing a cure for certain types of cancer in cases where a solitary tumor is present with no associated metastasis. During removal the surgeon will strive to obtain 3 cm margins in all directions of the tumor. This results in a large incision in relationship to the size of the tumor removed. In general the perimeter of the tumor contains the most aggressive cells, as they are the ones responsible for spreading the cancer to associated healthy tissues and increasing its size. To ensure that clean margins are obtained all removed masses should be submitted for histopathology. In cases where cancer cells are still present along the periphery, another surgery should be performed promptly or radiation or chemotherapy therapy should be instituted to reduce its ability to spread. In cases where masses do return they often are more aggressive than the initial tumor because as stated above the more aggressive cells at the periphery are what were left behind.
Radiation: Radiation therapy is the use of a very small narrow beam to deliver a dose of radiation, much higher than a typical x-ray, to treat cancer by interfering with the cancer cells' ability to divide and reproduce. Because beam location must be exact to target the area of the tumor, feline patients must be anesthetized to remain perfectly still. Therefore, it is important for the caregiver to understand that their companion will be undergoing repeated, short, durations of anesthesia. Once again, as with the chemotherapy mentioned above, this might not be an issue for some cats, however for others that are easily stressed or have concurrent health issues making them an anesthetic risk, radiation therapy might not be the best option.
Radiation therapy has a number of benefits. It can be used alone as a single therapy, or combined with surgery or chemotherapy. Radiation may be used prior to surgery to shrink the size of the tumor to assist the surgeon in obtaining larger clean margins when removal is performed, as well as after a surgery if clean margins were not obtained. In cases where a cancer involves the bone, radiation therapy can be instituted as a relief of associated pain.
Side effects of radiation therapy vary with the location being treated. The majority of felines will lose their hair where the beam is aimed. In contrast to chemotherapy some of these cats' hair will not grow back. Radiation could cause an inability for some tissue to heal resulting in skin ulcerations or sloughing of the skin. These lesions serve as a source of pain and therefore pain control should be instituted to keep the cat comfortable. Lesions typically do not develop until midway through the protocol. It is important to understand that stopping a radiation protocol too early can result in a drastic drop in the tumors ability to respond to subsequent therapy. Therefore, pain medication should be prescribed along with supportive therapy to aid the cat in finishing their prescribed treatment. One common location of cancer in geriatric cats is the oral cavity. The more common types of cancer at this location include, squamous cell carcinomas and fibrosarcomas. Surgical removal is not always an option in these locations due to the limited amount of tissue and the associated difficulty in closing the incision after tumor removal. In these situations, radiation serves as an option to control the growth and invasiveness of the tumor. When radiation is used in the treatment of these mucosal lesions the mouth could become dry or cracked and sometimes even cause drooling or a foul odor.
Immune-suppression: In situations where the above treatment modalities are determined as poor options, immune suppressive doses of corticosteroids could be instituted. There are a variety of reasons for the choice of this therapy either due to the extent of the cancer, concurrent disease, behavioral and personality limitations, or cost. Immunosuppressive corticosteroids serve as an inexpensive option that can inhibit the progression of the cancer, and can prolong the patient?s life and comfort. This therapy can be provided both inexpensively and through the comfort and convenience of home care. Corticosteroids are also associated with side effects, most commonly seen as gastric ulceration, increased hunger and thirst, as well as increased urination. When using corticosteroids there are two important general factors to recognize. One, you can never stop a corticosteroid abruptly. Instead you must gradually taper the dosage as prescribed by your veterinarian because when a corticosteroid is given (exogenously) the body's mechanisms (endogenously) to make its own corticosteroids is suppressed. Therefore, it takes time for the body to compensate for a decline in exogenous corticosteroid administration and to produce its own for body functional requirements. The second important factor when using corticosteroids is that it can not be combined with a non-steroidal anti-inflammatory drug (NSAIDS), which is commonly used in the treatment for pain. When used together these drugs produce a severe, hemorrhagic gastrointestinal ulceration that could result in gastric perforation. However, there is no benefit in ever using these two drugs together since corticosteroids work in a very similar fashion as NSAIDS and have a remarkable effect on alleviating pain of an associated tumor by reducing inflammation.
The number one goal of cancer therapy is usually not to cure the cancer, but to prolong the life of the animal in a comfortable fashion making pain control the number one priority. There are many drugs available to aid in doing this by reducing inflammation as mentioned above with either NSAIDS or corticosteroids. A common NSAIDS used in cats is Meloxicam. There has also been research that has indicated that this class of drug may have an inhibitory effect on cancer. The exact mechanism is not completely understood, however it is believed that the effect is stemmed from its cox-2 inhibition and its action against tumor producing inflammatory mediators. Other drugs used to reduce pain are within the Opioid family. There are assortments of drugs to choose from in this category allowing a wide variety of methods for administration. These drugs can be given as an injection, orally, or in the form of a patch. A fentanyl patch can be placed over a shaved region of the cat's body and will offer constant delivery of pain management for a three-day duration.
Unfortunately, the majority of geriatric cancer patients will eventually succumb to the disease of cancer either directly or from coexisting health factors. The dread of losing a companion can be a significant emotional burden for a caregiver and can be associated with depression, frustration, guilt, remorse, and grief. The bond between a companion and a caregiver is extremely powerful and during a battle with cancer there is a profound feeling of love and anticipatory loss. It is important to know that this is normal, and there is support available. In addition to the support of your veterinarian there are other resources to aid caregivers during this difficult time. Pet-loss counseling does exist, both on an individual basis as well as group therapy. Counseling is available for free at many veterinary universities through the form of a hotline service. There are also pet cancer support groups on the internet that allows caregivers the opportunity to share both their experiences and feelings in a safe peer group.
Although at times aiding a companion in their battle against cancer can seem overwhelming, the experience can also be very rewarding. Cherish the time you spend with one another and pride yourself on the ability to care for and relieve your companion from pain. The connection between an animal and human is a unique and cherished relationship that should be honored and treasured.
The Animal Medical Center -- Human-Animal Bond Programs
New York, (212) 838-8100
Discussion group: www.amcny.org
The Pet Loss Grief Support Website
University of Florida -- Grief counseling
(352) 392-4700, 1+4080
Washington State University -- Pet Loss Hotline
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Fidel, Janean DVM: VM 552 Small Animal Medicine notes, Oncology. Washington State University. February 2009.
Marretta JJ, Garrett LD, Marretta SM: Feline oral squamous cell carcinoma: and overview. Vet Med. June 2007.
Milner RJ, Peyton J, Cooke K, et al: Response rates and survival times for cats with lymphoma treated with the University of Wisconsin-Madison chemotherapy protocol: 38 cases (1996-2003). J Am Vet Med Assoc 227:1118. 2005.
Villalobos, Alice DVM, Laurie Kaplan MSC. "Canine and Feline Geriatric Oncology, Honoring the Human-Animal Bond" Blackwell Publishing. 2007.
This paper is dedicated in loving memory to Edd.