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Simply put, chemotherapy is the treatment of cancer with drugs. These days, there is a diverse and broad range of medications, but the purposes and principles of treatment are still the same. Chemotherapy is usually the primary treatment for systemic tumors, such as lymphoma, leukemia, or multiple myeloma. It is also the principal treatment for solid tumors that have spread to multiple distant sites. Chemotherapy can be given at higher doses with the hope of potential cure. This is applicable to certain tumor types and situations but not all. In others situations, it can be given for palliative purposes, which means to relieve suffering and improve a patient’s quality of life for an extended period of time.

Chemotherapy can be administered neo-adjuvantly to shrink a tumor, with the hope that a different treatment – surgery or radiation – can be then be used to completely remove the tumor. It can be used in an adjuvant fashion in addition to surgery or radiation, with the hope of preventing spread/growth of disease at other sites in the body. It is sometimes though less commonly used when a tumor is incompletely removed. The best option in this situation usually is a second surgery or radiation if the mass is unlikely to otherwise spread elsewhere.

How does it work?

In general, chemotherapy drugs are most active against rapidly dividing cells, particularly cells in specific phases of the cell cycle. Chemotherapy is thus most effective when used against rapidly growing tumors. Some tumor types have a high growth fraction and are known to be very sensitive. For most, however, they have a much higher growth rate when they are smaller and less when they grow large. In smaller tumors, chemotherapy is more effective in getting to all parts of the tumor. There has been less time for cells to mutate into drug resistant subpopulations in the tumor, and there are a lot fewer cells to kill. With larger tumors, surgery or radiation can be used to reduce the total tumor volume to make chemotherapy potentially more effective. Ideally though, early detection and treatment are keys.

What is metronomic chemotherapy?

Traditionally, chemotherapy is given at the highest possible dose with the idea that this provides the highest concentration of drug to the tumor and provides the greatest effect. Giving high doses, however, requires time between treatments for the body’s normal tissues to recover. Some organs have higher cell turnover and growth rates than others. These include the gastrointestinal tract and bone marrow. In humans and in some breeds (poodles, for example), this also includes hair. With traditional dosing, a break of 1 to 3 weeks is required. During this time, cancer cells also recover.

A second treatment strategy uses dose frequency instead of dose intensity. Low-doses of chemotherapy are given frequently over a long period of time. Benefits are sometimes lower costs and lower risk of toxicity. These metronomic treatment protocols are still being investigated for effectiveness, and there is currently less research supporting their use than traditional treatment. However, this may change in the future. Most likely, a combination of treatment types will be recommended depending on the tumor and particular situation. With metronomic or anti-angiogenic treatment, tumors also don’t shrink quickly or may not shrink at all. The hope instead is they don’t grow and remain stable for extended periods of time.

What is anti-angiogenic treatment?

For a tumor to grow beyond a few millimeters in size, the tumor needs to grow “supply routes” to feed itself. These supply routes are new blood vessels that supply the tumor with oxygen and nutrients and remove waste by-products. If one can interfere with the growth of these new blood vessel supply paths, one can effectively keep a tumor in check by limiting the size it can grow. Much research has been done to find a variety of agents designed to prevent new blood vessel growth. These drugs are called anti-angiogenic. Some specifically target growth receptors, such as platelet derived growth factor (PDGF) receptor and basic fibroblast growth factor receptor (BFGF-2). Traditional chemotherapeutics can also be used as anti-angiogenic agents. Even some non-steroidal anti-inflammatory drugs have potential anti-angiogenic properties as well. To date, anti-angiogenic treatment is promising but better viewed as treatment option that augments traditional strategies as opposed to the primary treatment strategy for most tumor types. A combination approach to treatment is still optimal for most situations.

Monitoring Patients

Prior to treatment, we will review with you expectations for treatment and potential for toxicity. Most side effects are mild-to-moderate and self-limiting with preventive medications. It is our goal to have our patients experience the highest quality of life possible. That means that our patients look, act, and feel like normal, healthy dogs.

CBC

At a set interval after treatment, usually 7 days, we recommend a complete blood count (CBC). A white blood cell called the neutrophil is most commonly affected by chemotherapy, and counts predictably reduce about 5 to 7 days after treatment. This reduction is temporary and recovery is rapid. However, for a time, antibiotics might be needed for prevention of infection, since neutrophils are important for preventing such infections. If a particular drug causes severe decreases in neutrophil counts, the dose may be reduced on future treatments. A CBC is also performed prior to the next treatment. If neutrophil counts have not recovered, treatment may be delayed. Sometimes, platelets decrease. This occurs with certain drugs, such as lomustine (CCNU) or Carboplatin. This is rarely a reason for treatment delay. Red blood cell counts are often reduced in patients with cancer. However, in veterinary patients, the cancer or other illness is more commonly associated with sudden decreases in PCV (red blood cells) than cancer treatment. Thus, when a patient becomes more anemic, we are more concerned about internal bleeding or cancer progression depending on tumor type.

Serum chemistry profile

This is performed prior to treatment and at certain points during to monitor factors associated with kidney and liver health. Drugs are metabolized in the body and eliminated through these organs. Thus, checking for their continued health is important. Some tumors also cause abnormalities such as elevated calcium. These levels can also be checked to monitor treatment progress.

Other tests

Ultrasound, radiographs, CT scan, and/or fine needle aspirates or biopsy may be recommended periodically to monitor treatment progress as well. These are individualized to the tumor type, location, and case.

Surgery is an important part of cancer treatment and can cure more patients than any other form of treatment. This is true because surgery is usually recommended for solitary, early stage masses that have not spread much beyond the primary site. We sometimes say “a chance to cut is a chance to cure.” However, for surgery to be effective, it must be planned and performed appropriately so that residual tumor - even if microscopic - is not left behind in the patient. Tumors often spread far beyond what can be detected by physical exam alone. While small, localized tumors are easier to completely remove, larger ones or ones in “tight” spots, such as the mouth, require more advanced planning. For these, additional diagnostics, such as CT scan, are often recommended.

To help with treatment planning, your veterinarian may first perform an incisional biopsy or fine needle aspirate to determine the specific tumor type. These procedures are not performed with any curative intent. The information is useful because different tumor types behave differently. For example, sarcomas and mast cell tumors are locally invasive and need more tissue removed around the tumor to achieve complete removal of the masses.

Sometimes tumors are too large to completely remove with surgery alone. Options then include (1) palliative radiation or a debulking surgery to reduce the tumor size for as long as possible to improve a patient’s life quality or (2) surgery in addition to radiation to remove most of the tumor and then treat the residual disease with radiation. Recommendations are based on tumor size and location, client factors, and tumor type. Debulking surgery and palliative radiation are temporary measures to improve a patient’s life. They are not cures. Performing surgery in addition to radiation is recommended with the hope of cure.

Clients are often fearful of anesthesia and surgery, most particularly because of a pet's age. Age, however, is not a disease, and a healthy older dog is likely to do as well as a healthy younger one. Prior to surgery, the doctor performs a physical examination, lymph node evaluation, blood work, and urinalysis to determine the health status of the patient and to identify other disease states. Additional staging diagnostics such as 3–view chest x–rays, CT scan, abdominal ultrasound, or cardiac evaluation are sometimes performed to evaluate potential spread of disease and determine fitness and health. Problems found are discussed with the client prior to surgery so the best treatment decision for a particular patient can be made. Pre-surgical evaluation helps to minimize risks and determine whether surgery should be recommended at all.

Specific surgical techniques have been developed for treating tumors. For larger tumors or tumors in tough spots, we recommend board-certified surgeons to perform definitive surgical treatment, though there are many excellent general veterinarians who have extensive surgical experience. You should talk with your veterinarian about her or his comfort with a particular procedure to determine the appropriate treatment course for your pet. A good first surgery is an important factor for improving a patient’s long term outcome.

In addition to, or as an alternative to traditional treatment options, we provide recommendations and therapies designed to alleviate pain and improve quality of life. We provide information about a variety of different therapies for pain management, appetite stimulation, and nutrition. We provide recommendations about exercise, daily care for your pet, and preventing adverse side effects associated with the cancer or with treatment.

Radiation is one of three main treatments for cancer. It can be used as the sole form of treatment. Usually, it is recommended in addition to other treatment strategies. It can be used before or after surgery of a large, invasive tumor to slow or prevent re-growth from small pockets of cells that have been left behind. It can be used to shrink large, sensitive tumors that are significantly affecting life quality. It can be used when tumors are in places that are hard to remove or in which removal can cause significant cosmetic defect. Side effects are usually limited to the tumor site. Radiation sickness seen in human medicine is less common or not seen in veterinary patients.

Radiation is usually performed in one of two ways. Palliative radiation involves the administration of a few weekly treatments using large doses (fractions) per treatment. This type of treatment has fewer short-term side effects, but longer term side effects (one year or later) may be severe. Definitive or full-course radiation involves giving smaller, frequent doses of radiation. Usually these treatments are performed 3 to 5 days per week for 3 to 4 weeks. Each treatment lasts about 10 to 30 minutes. Patients must be still during treatment, so sedation or anesthesia is required. However, patients are monitored closely, and while there are risks associated with anesthesia, they are minimized as best possible.

Side effects:

Your pet will lose hair in the irradiated field only. It grows back in about 3 to 6 months, though it grows back a different color and texture. Moist dermatitis (“radiation burn”) commonly occurs toward the middle to end of treatment. This lasts about 2 weeks, and medications are given to minimize discomfort to your pet. It's important to keep your pet from scratching or rubbing the site. The muco-cutaneous tissues (such as the tissues of the mouth) are already sensitive, so radiation burn may be more severe in these locations. With mouth lesions, soft, low-salt foods are recommended for feeding for 2 to 3 weeks following treatment. Mouth rinse may also be prescribed. Sometimes reactions are severe, but this occurs in less than 5% of all cases. If the eyes are in the treatment, lead shielding can sometimes be used. If not, a cataract will form, and the patient will lose vision in that eye in 6 to 12 months.

A variety of factors determine whether a tumor will respond to radiation treatment. Tumor size, type, and location are all important. For most tumors, no change in tumor size may be apparent for weeks. Only a few very sensitive tumor types will respond quickly. Therefore, debulking surgery may be performed in addition if a tumor is seriously impinging upon a patient’s quality of life.

We are here to help you and your veterinarian understand different therapeutic options and learn about possible state-of-the-art therapies. We perform research and collaborate with other researchers in the oncology community at large to provide personalized cancer treatment for your pet.

We participate in research, and are active members and collaborators with a variety of organizations, including the Veterinary Cancer Society (VCS), American College of Veterinary Internal Medicine (ACVIM), Veterinary Eastern Cooperative Oncology Group (VECOG), and the Veterinary Clinical Investigations Center (VCIC) at the University of Pennsylvania, among others.

We use and are involved in the evaluation of novel drugs such as Palladia and Masitinib, and we have been and currently are still involved in studies to evaluate novel treatments for mast cell tumors, lymphoma, melanoma, bladder tumors, mammary tumors, and canine hemangiosaroma.