Chemotherapy Principles For Dogs And Cats

I was having a discussion with a devoted pet owner shortly after she overheard a client in our clinic lobby say that she “spent $1000 to get her dog’s right knee fixed and she wasn’t going to spend anything on the left one.”

Tucker had surgical removal of a mass, which turned out to be Mast Cell Tumor. Then it spread to a lymph node. Now he is having chemotherapy.

A devoted pet owner, we’ll call her “Frieda,” overheard, and was incredulous, saying that she would do almost anything for her pets, “but chemo,” she continued, “wouldn’t be fair to them because they don’t understand.”

It is a common mistake to think of cancer chemotherapy in terms of human treatment. It’s what we know. It’s what we see when we go to work, to the store, to church. We see bald men, women with wigs, children with no hair. We see burns from radiation.

We hear stories of (or have experienced with our own loved ones) vomiting, diarrhea, total loss of appetite, life-threatening infections. We hear stories of people who undergo horrible suffering because of their will to live.

We think that dog chemotherapy and cat chemotherapy must be the same.

It isn’t.

Let’s look at what it is.

The root “chem” stems from the Greek word, chemeia, which has roots to alchemy, a Middle English word. In medieval times alchemists sought to transform base metals into precious ones, such as gold and silver. In chemotherapy, “chemo” is short for “chemical.”

“Therapy” comes from the Greek therapeia, meaning to cure or to heal.

Literally, then, chemotherapy is the use of any chemical element or compound for the treatment of a disease. The disease need not be cancer. Every time we take an antibiotic for a urinary tract infection or sinus infection, we are being administered chemotherapy.

Languages evolve, and usage defines definition. Today, the word chemotherapy is inextricably attached to the treatment of cancer in the layman’s mind.

The most important difference to understand between cancer chemotherapy for humans and cancer chemotherapy for domesticated animals is the goal of treatment.

People suffer many cancers that can be cured, permanently eliminated from the body. Humans also experience many cancers that can be controlled by medication, extending life expectancy even in the absence of  a total cure.

Cancer in pets is different. There are some cancerous growths that can be cured with surgical excision. Some respond to radiation, never to return.  Curative doses of chemotherapeutics, however, are rarely used in animals. Let’s look at the reasons:

  • Pet owners and pet doctors have little tolerance for animal suffering. Agents (drugs) and doses of agents that cause severe weakness, vomiting and diarrhea are avoided.
  • The human medical care system is well-equipped to provide nursing vigilance for the debilitated and incapacitated cancer patient. Usually, owners of pets provide all at-home aftercare, so dogs and cats simply are not allowed to become ill to a comparable level.  Who could care for them, clean them and provide that level of nursing for the duration of their treatment?
  • Cost. Out-of-pocket expenses can be high. Some pet health insurance policies do not provide coverage for cancer at all. Some companies may place limits on payments for cancer treatment. One factor to consider is treatment variables. Although each type of cancer is treated differently, there are protocols that cost a considerable amount, and there are those that are downright inexpensive. Of course, the more costly medications carry the best prognosis, but a shortage of funds doesn’t mean that treatment is out of the question.
  • Quality of life. The philosophy of many board-certified veterinary oncologists is summarized in this statement by Dr. Elizabeth Kergosien of the MedVet Mandeville Medical & Cancer Centers for Pets, on chemotherapy, “Our goal is that the patient will not experience even one bad day.”

If your pet has cancer, remember that there is cure for some types of malignancies. If your pet’s doctor suggests chemotherapy, he can explain exactly what side effects to expect for the specific treatment(s) your dog or cat will have. Ultimately, you are in control, and you can determine the experience your pet will have, according to your tolerances.

Chemotherapy in pets is about buying time, and making that time be excellent quality time.

See you Monday, Dr. Randolph.



  1. Our 10yr. Old Bailey was diagnosed last July with cutaneous lymphoma. A wonderful skin/allergist made the diagnosis after taking skin scrapings and sending them to her lab. Both she and our caring vet recommended consulting an oncologist they knew. We were so devastated when we got the diagnosis, as Bailey had been the healthiest dog we had ever had. Her only symptom was a tiny spot of hair loss that got larger very quickly. The oncologist suggested a chemo pill that we take her in for every three weeks. She gets blood work at the same time . She is also on daily prednisone, denamarin to help protect her liver, and a fish oil capsule for her coat. We are five months in and she is doing great. Her coat is shiny and lovely. Thin on her underside, but since starting the chemo her top coat looks amazing. Our family and friends can’t believe how great she looks, and she can still run like a young puppy. I have my walking companion back at least a few days a week. The only downside we have is that the prednisone makes her drink more, and therefore she goes out at 1 a.m. and again at 5. She used to sleep a good 12 hrs. nonstop. We tried cutting back on both the prednisone, and doing the chemo once a month. We had to go back to every three weeks and up the prednisone. We know at some point this will all stop working, but it has given us several extra months with our girl. We were very fortunate to have had this checked out and diagnosed right away. We were told one to two months without the chemo.I hope this information is helpful to someone. We are fortunate to have great specialists in our area who are not only the best in their fields, but also unbelievably compassionate. We were shocked to learn how rare this cancer is and that there is no cure.

    • What a great success story! Thank you for sharing it. Often, people hear “chemo” and immediately close their ears to anything else. Chemotherapy in dogs and cats is inherently different from chemo in people, and, if a pet owner is in the position to consider treatment for cancer, you owe it to yourself and your pet to at least consult with a board-certified veterinary oncologist to find out what your pet’s options are and what the possible side effects, prognosis and anticipated outcome are. In your short comment, you may have encouraged countless people to do exactly that. Thank you for your outreach, Dr. Randolph.

  2. Our 8 year old golden was diagnosed with a mast tumor on his left hip area. Just popped up quickly. Testing determined the cancer was not found elsewhere (for now). Mass removed and during surgery second, smaller mass found below and was removed. Cullen is recuperating nicely and in true golden fashion, happy all the time. We were surprised at the length of the incision. We are now reviewing options. And am leaning towards the pill chemo which the vet oncologist recommends. Question to all those fur Parents who went thru this. When you decided to do chemo, how much longer from time of diagnosis did your fur baby have or continues to have a good quality of life ? Realize there are variances due to many factors but trying to get some idea of what the future could be. I keep saying I wish I could make it go away (for all pet parents) but unfortunately not possible. We appreciate your response

  3. This is Tucker’s Mom. I wanted to add more information about the treatment options and our decision. It was hard for me to find this sort of information online, so I hope that this may be of use to others. Tucker’s oncologist (Dr. Elizabeth Kergosien) is fantastic and she provided us with the information we needed to make a decision that was right for both Tucker and us. Here is our story.

    Tucker had mast cell cancer that spread to a lymph node. This means it had metastasized, and radiation is not the recommended course of treatment. Radiation costs can be in the thousands of dollars for treatment and it usually used to get rid of any extraneous cancer cells after a surgical removal of a tumor. It was not appropriate for Tucker’s situation because his cancer was assumed to have spread widely throughout the body. We were glad we didn’t have to make a decision about such expensive treatment.

    We had three options for treatment.

    1) Least aggressive chemotherapy. This is the most common and easy treatment and has few side effects. It’s inexpensive, less than $50 per month.

    2) Chemotherapy with one or more drugs in addition to (1) above, and medicine to help protect the gastric system. This would cost about $300 – $450 per month (at 3-week treatment intervals) including bloodwork to monitor potentially harmful side effects. Add to this the cost of option (1).

    3) Testing to stage the cancer (appx. $600-$700), surgical removal of the lymph node (appx. $700-$1000), then chemotherapy via option (2) and continue option (1).

    Mast cell cancer is known to be unpredictable in its advancement and response to treatment, so averages on life expectancy are just that: averages. There is a wide range of possible outcomes. With that in mind, the oncologist told us that with only option (1) as treatment, Tucker probably had 6 weeks to 6 months before the cancer makes him so sick that we would have to euthanize him. With the most aggressive treatment, option (3), and a very good outcome from it, he would have 6 months to 1 year. The chemotherapy does not produce any results in about 50% of cases, and in the 50% of cases that it works, it does not cure the cancer. It only slows it down. There are always exceptions and we hope our dog will be one of the lucky ones. Making a decision on treatment is essentially gambling. We have to compare the cost of treatment in the form of money and quality of life, with the reward of a longer quality life.

    With regard to how these treatments would affect Tucker’s quality of life, option (1) was a no-brainer. It’s cheap, easy, and the side effects are mainly an increase in Tucker’s appetite and water intake. Those are minor and we started medication (1) at Dr. Randolph’s recommendation immediately. His swollen tumor decreased in size within 2-3 days. We are continuing this treatment throughout. Surgical removal of the lymph node could be problematic. Due to the physical construct of the tumor and the nature of mast cell cancer, there could be difficulty healing. We were very surprised to find out that chemotherapy does not make dogs sick as it does humans. Dr. Kergosien said that many dogs have no noticeable side effects at all. It can cause severe gastric problems, but that is the exception rather than the norm. This was good news.

    So how did we decide what to do? Before we had any of this information, we had already decided that with Tucker being 10 years old and mast cell cancer being aggressive and terminal, we didn’t want to put him through a long, drawn-out unpleasant treament in hopes of buying him time. What if we took our happy dog and made him sick with treatment only to have the outcome be that he didn’t respond to treatment? He is feeling good now, and we didn’t want to risk taking that away from him. We immediately ruled out option (3) for treatment because of his previous gastric problems, age, and mostly because it seemed like it would be too hard on Tucker in exchange for the hope of 6 more months at best. Sticking with our original wishes, we chose option (2) after finding out he could probably get chemotherapy without illness. We could afford the treatment. We chose a pill form because it is the least likely to cause gastric problems, and Tucker has a history of gastric problems. The other drugs were ruled out mostly on that basis. We thought the cost was reasonable for the 50% chance that it could buy him 3-6 more months of quality life. There is a small chance that he’ll be one of the lucky ones and live much longer than that. If the pill makes him ill, we’ll quit. But so far, so good. It’s 7 days after his first treatment and other than a bit of gas one night, we see no side effects. He’s wagging his tail, enjoying his food, and feeling good so far as we can tell.

    • I have been following your treatment of Tucker. Many thanks for your logs. My Dixie had mast cell cancer that was ulcerous and fast growing in the lower abdomen region 6 months ago and there was enough skin to cut out the tumor and large areas around it and the vet said he was able to get good clearance around the entire area. Dixie healed up and has been a perky happy little 8 year old. Last Thursday I found another lump at her rear mammary gland that is hard and the size of an egg, it came up over night. We took her back to the vet, ran blood work,aspirated the lump took x rays and will be getting a ultrasound tomorrow. We suspect this is in her lymph nodes and I fear the worst. I too worry about Quality of life over quantity of life and will choose Quality. If offered ( and I will ask) I will go with your option 1. I am hoping you will see this and tell me how option 2 went. I am so scared right now. We lost Dixie mate to a sudden heart attack at 10 just a year ago and we are All still reeling from losing Mr. Merlin.

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