Chemotherapy for Dogs

Picture of a grey dog sleeping

There are three main ways of treating cancer in dogs: surgery, chemotherapy, and radiation therapy. Depending on the type of tumor that a dog has developed, one or a combination of these treatments could be effective.

In today’s article, we’re looking at the most important facts about canine chemotherapy, from how it is administered to the side effects it can have.

What is Chemotherapy?

While surgery refers to the physical removal of a tumor and radiation therapy refers to treating the neoplasm using radiation, chemotherapy involves medication.

Some drugs used in chemotherapy can be synthetic versions of those extracted from plants, while others can be purely synthetic and might be administered based on a variety of studies.

Choosing the right type of cancer therapy involves two or three people – the veterinarian, the pet parent, and sometimes, the veterinary oncologist. It is important to have a talk and assess the severity of the cancer, the stage it has reached, as well as its malignancy potential to understand whether chemotherapy might be a viable option or not.

The pet owner also has to express consent for any of the elected therapy (often in writing) and must be informed about the adverse reactions that these medications can have on their dog. Quality of life during the treatment is of utmost importance, and that is why the dog’s general health status must be assessed regularly to ensure that the chemotherapy dosage is adjusted appropriately.

What types of cancer can chemotherapy help with?

This type of treatment alone typically proves its worth in several main cancers — lymphoma, leukemia, myeloma, as well as transmissible venereal tumors.

Many other cancer types can be treated, or at least their therapy can be aided by chemotherapy, but it is usually not the only treatment that is involved.

Types of Chemotherapy for Dogs

There are three main different kinds of chemotherapy, and they are categorized as such depending on their effects:

  • Adjuvant
  • Neoadjuvant
  • Palliative

Adjuvant chemotherapy refers to the medical treatment that a patient that has had cancer and has been operated on needs to receive. If the dog has metastatic cancer, it is assumed that chemotherapy will kill the neoplastic tissue that might have remained or that might have been impossible to remove during the surgery. Adjuvant chemotherapy works best for cancers such as mammary, bladder, and thyroid tumors, or for hemangiosarcoma and osteosarcoma.

Neoadjuvant chemotherapy is relatively new, and it refers to the initiation of the medical treatment before the surgery. This can often help with a significant reduction in the size of the tumor and a decrease in its invasiveness. This approach works for mast cell tumors and lung tumors.

Palliative chemotherapy refers to cancers that are typically inoperable. Administering these medications will improve the pet’s quality of life and will also lead to them living for a longer amount of time. Some types of anal sac tumors, mast cell tumors, as well as bladder cancers might have to be ‘treated’ with this method.


Various medications exist nowadays as part of a chemotherapy process, and they can be administered differently.

For many years, only the IV administration was considered effective and was heavily relied on. However, depending on the cancer type and whether oral drugs cater to its treatment or not, they can be another choice.

IV drugs such as vincristine have to be administered regularly, whether a dose per week or more often, in the beginning. An intravenous catheter is placed and removed after the medication is administered.

Oral medications can be given by the pet owner at home, but there are some safety factors that have to be considered. The pet parent is typically advised to wear gloves so as not to put their skin in contact with the drug. Also, the capsules do not have to be crushed or the pills split. Hiding the medication in peanut butter or the dog’s favorite snack is quite helpful.

Oral drugs are easier to administer, and the pet doesn’t have to go through the experience of being taken to the vet clinic as often as if they were administered IV medications.

Is Canine Chemotherapy Safe?

Most of the medications involved in the treatment of cancer are safe, but the dosage has to be tweaked depending on how the pet’s body responds to them.

Because cancer is developed in the body’s cells, chemotherapy has to be cytotoxic (it has to have the ability to kill the cells). For this reason, there are a number of adverse reactions that can happen.

The two main organs that these drugs can affect negatively are the liver and the kidneys, as these are the ways the medications are eliminated from the dog’s body. As such, the veterinarian has to perform blood tests on a regular basis to make sure that the animal’s hepatic and renal functions are not severely affected.

Common Side Effects of Chemotherapy for Cancer in Dogs

If we were to look on the bright side of things (if there is any when it comes to cancer), it would be that pets tend to experience fewer side effects to being treated with chemotherapy than people do.

Vomiting and diarrhea are the two most common symptoms that can be seen in pets that experience adverse reactions, along with nausea, changes in their appetite for food and water, and lethargy.

Long-term side effects can also be seen in some pets, which means that even if they might feel mildly unwell after the administration of the medication, they could experience the full impact of the drug about 5-6 days after the chemotherapy session.

Pet owners and vets have to communicate constantly to make sure that they maintain the dog’s quality of life as best as possible. This could mean that the dog might have to be seen and tested by a vet every week.

Does a Dog’s Hair Fall out During Chemotherapy?

Alopecia is a common side effect that humans experience with chemotherapy, but it is not as common in our canine friends.

In fact, most of the dogs that do get to develop localized or generalized alopecia are long-haired breeds such as Poodles or Cocker Spaniels, and their hair grows constantly. For this reason, excessive shedding might indeed affect these breeds.

How Long Does Chemotherapy Last?

This is a question that is very hard to answer since it depends on the pet’s health, age, and other factors, as well as the specific type of cancer they have. Some cancers can be treated easier than others, so the number of sessions might be lower in that situation.

Adjuvant chemotherapy is often administered for at least several months following the operation. Neoadjuvant chemotherapy is the same, but it is typically given before the surgery with minimal doses (and over the course of a shorter time span) following it. Palliative chemotherapy involves the administration of medication for the rest of the dog’s life, if their tumor is inoperable, with constant modification of the dosage.

As for the cost of the sessions, it also depends on the treatment length and the medication used. Some types of pet insurance can help with the expenses in some cases.

Final thoughts

Even though no one wants to consider chemotherapy as a treatment option for cancer, sometimes it can be quite effective, especially when combined with other methods such as surgery.

It is important that the pet owner and the veterinarian stay in close contact to make sure that the dog remains as healthy as possible all throughout the therapy.

This cancer treatment might also not be appropriate for some dogs, so having an honest conversation with the vet and the veterinary oncologist can help pet parents make the right decision.



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