Everything You Ever Wanted to Know About Pet Chemotherapy

August 25, 2020

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Chemotherapy is a very important treatment modality used for many types of cancers in dogs and cats. It has been applied in different ways including as sole treatment for certain systemic cancers such as lymphoma and leukemia with the goal of achieving remission. Chemotherapy has also been used in combination with other treatments:

–to shrink tumors before surgery or radiation therapy (neoadjuvant therapy)

–to delay or prevent metastasis (spread from the primary cancer to other parts of the body).

–after surgery or radiation therapy (adjuvant therapy).

Additionally, chemotherapy is often used to help alleviate clinical signs and improve quality of life of pets.

Not all drugs that treat cancer work in the same way. Traditional, also known as standard chemotherapy, is designed to kill rapidly dividing cancer cells (cytotoxic).  This is done by blocking various stages of cell division. Targeted therapy drugs (technically chemotherapy) focus on targeting some of the changes that make cancer cells different than normal cells. Targeted therapies may work by blocking the formation of blood vessels (blocking nutrients and oxygen). This causes tumor cells to “starve”, blocking off chemical signals and prevent tumor cells from growing and dividing or by triggering the immune system to kill cancer cells.

In many cases, a combination of drugs is the most effective way to kill cancer cells.  That is because different chemotherapy drugs have different targets. The best choice of chemotherapy doses and treatment schedule will depend on the type and stage of your pet’s cancer. In some cases, the chemotherapy regimen is based on well-known research studies. In other situations, less may be known about the best strategy to treat certain types and stages of cancer.

Chemotherapy and potential side effects

As mentioned, chemotherapy drugs kill fast-growing cancer cells.  But, the body also has healthy cells that are naturally fast-growing cells. The normal cells most likely to be damaged by chemotherapy include blood-forming cells in the bone marrow, hair follicles and cells lining the gastrointestinal tract. Side effects that commonly occur are vomiting and diarrhea, low white cell count (from bone marrow suppression) and occasionally, hair loss.

Chemotherapy is generally well tolerated in dogs and cats.  Most do not experience side effects. Some pets will experience mild lethargy/weakness, decrease appetite and a few episodes of vomiting and/or diarrhea. These side effects will typically last for a few days and are managed on an outpatient basis. Some patients (roughly 5%) will experience more significant side effects necessitating hospitalization and supportive care. Fatal side effects from chemotherapy are reported to occur in less than 1% of patients.

Our goal is to provide you with as much information as possible to help guide you in deciding whether chemotherapy is right for your pet. Below is a list of some of the most common questions regarding chemotherapy for pets

How often is chemotherapy given?

Chemotherapy schedules are tailored based on each individual patient’s needs. Some treatments require daily (oral drugs) or weekly administration (typically injectable drugs).   Others may be repeated every 2 to 3 weeks depending upon the tumor type and stage present.

How is chemotherapy administered?

Chemotherapy drugs can be administered as follows:

  1. Intravenous: given directly into the vein (most common way chemotherapy is administered).
  2. Oral: given by mouth (pill form)
  3. Subcutaneous: given under the skin
  4. Intralesional: given directly into the tumor or surgical site
  5. Intramuscular: given into a muscle
  6. Intracavitary: give directly into the chest or abdomen

What is a chemotherapy drug protocol?

A chemotherapy drug protocol refers to a set regimen of drugs given at a specified time interval. It may include one main drug or multiple drugs.

How long will my pet receive chemotherapy?

The length of chemotherapy treatment will depend on the type and stage of cancer. Many chemotherapy drug protocols involve a series of treatments followed by a careful period of observation. Some patients (primarily those with advanced disease) may continue to receive chemotherapy for as long as it is controlling the cancer.

When would side effects be seen in my pet following chemotherapy?

Most pets receiving chemotherapy experience minimal to no side effects. This is mainly due to the drug dosages and treatment schedules used in veterinary medicine. Side effects most commonly occur 2-3 days following treatment .  But, they could occur the day of treatment until 10-14 days later.

What are common side effects my pet may experience with chemotherapy?

  1. Common gastrointestinal side effects include:
  • Nausea, vomiting, diarrhea and constipation; most of which can be readily controlled with medications and/or diet change. These side effects may last between one day to several days
  1. Common bone marrow side effects include:
  • Decrease in white blood cells and at times platelets
    • White blood cells are very important in fighting infections. If a pet’s body has a very low white blood cell count, it is susceptible to developing an infection.
    • It is important to know that not all pets with low white blood cell count will develop an infection. In fact, most pets feel well and have no clinical signs at all despite their low white blood cell count.
    • If a pet spikes a fever, acts lethargic or refuses food, then hospitalization and supportive therapy are necessary.
  1. Hair loss is common in people, but rare in dogs. Hair loss can be seen in pets with constantly growing hair (i.e. poodle, shih Tzu). Cats generally do not lose body fur but may lose their whiskers.
  2. Some chemotherapy drugs can cause irritation to the skin and surrounding tissue under the skin if they leak outside of the vein during injection. Severe swelling, ulceration and inflammation can be seen. Our veterinary technicians are carefully trained in proper handling and administration of chemotherapy to our furry patients.
  3. Some chemotherapy drugs have unique toxicities. These side effects will be explained to you in detail at the time of your appointment, if we recommend any of these drugs to your pet.

How expensive is chemotherapy?

Our goal during your pet’s appointment is to develop the best diagnostic and treatment plan possible. The recommended plan is based on the type and stage of cancer. At The Cancer Center at AVCC, we strive for everyone to be well informed about their pet’s diagnosis. So, we work closely with every pet owner to tailor a plan that meets both your pet’s specific treatment needs, as well as your financial needs. We also provide written summaries that detail the frequency of visits and costs involved.

What happens when chemotherapy no longer controls the cancer?

Most cancers are initially very sensitive to chemotherapy drugs. In some cancers, complete remission following chemotherapy is possible. In other instances, only stability of the disease and improvement of their quality of life is obtained. Relapse or progression of the cancer can be seen in weeks, months or even years later, due to development of resistance to chemotherapy. We can often use other drugs.  But, each time resistance develops it is difficult to find a drug that the cancer will respond to. Our goal is to provide a good quality of life for your beloved pet while on chemotherapy and after. If all cancer treatment options have been exhausted, we will work closely with you, to help manage your pet’s comfort and well being.

For more on cancer treatment for your pet, see our Comprehensive Guide to Pet Cancer Care.

The Cancer Center at AVCC is located in South Florida in Broward County.
8920 W. State Road 84,
Davie, Florida 33324


The Cancer Center at AVCC offers the following oncology services:

Diagnostic tests including:

  • Fine needle aspirates/cytology
  • Bone marrow aspirates
  • Bone biopsies
  • Incisional and punch biopsies
  • Personalized genomic testing


  • Traditional chemotherapy (intravenous/intracavitary)
  • Metronomic chemotherapy
  • Targeted chemotherapy
  • Immunotherapy
  • Palliative care and pain management
  • Hospice counseling
  • Nutritional counseling and referral
  • Referral for pet radiation therapy

Keep your paws on the latest pet news, food recalls, safety tips and more from the board-certified veterinary experts at Advanced Veterinary Care Center in Davie.

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