Chemotherapy in Pets?


By John Andersen, DVM

There comes a time when we all will realize that our pets have gotten old. Sometimes, it’s a sudden and surprising catastrophe after seemingly endless years of perfect health. Other times, it’s just a matter of realizing that the gray around your dog’s muzzle is growing with each passing season.

This realization just hit me a few weeks ago when I diagnosed my own 10-year-old dog with leukemia. She has been in such good health her whole life that I figured she’d at least make it to 15 or 16—after all, she’s owned by not one, but two veterinarians! I always thought we’d somehow have more control over her health, and be able to diagnose and cure any condition quickly before it became too serious. But as a dog owner, I’m really not much different from the next.

It’s hard for anyone to separate what is normal “10-year-old dog” behavior from what is “maybe my dog is sick” behavior. For instance, over the past few months, she had gradually been sleeping more and more under the bed on my wife’s side. Ten-year-old dog, or sick? She had also been eating a bit slower, but usually still finishing all her food by the end of the day. Normal for an old girl … or is she ADR (ain’t doin’ right)? Also, I had clipped her coat pretty short about a month ago, and it was then that some of the glands under her jaw felt more prominent—not huge, just more prominent. Were they always like that?

And it’s hard to feel like there’s something wrong when your dog is so excited to see you whenever you come back home (even if you just checked the mailbox). Or when they would never turn down a treat or a walk, or still do those annoying but endearing “character traits” – like nudging your elbow when your cup of coffee is full.

Ultimately, nobody knows your pets like you do. With more prodding from my wife than from me, I took our former Roanoke SPCA mutt (priceless now, of course) in to work with me, only to find out that her white blood count was twenty times the normal range—consistent with leukemia. In one day I was saddened and surprised that my girl had somehow gotten old on me.

My point is to say that if you feel like your older dog or cat is just not right, get them checked out. Hopefully, they’re just getting older. But dogs and cats are very talented at hiding signs of serious diseases. It’s just not in their nature to advertise that they’re sick. Survival of the fittest is a tough world.

I want to talk about chemotherapy for cancer treatment in dogs and cats. Many people may feel that only crazy people would do such a thing, or that it’s unfair to the pets, or that you’re simply beating a dead horse. But let me just say that our old girl is feeling pretty good and has a totally normal white blood cell count after just two weeks of pretty reasonable chemotherapy.

Still, whether to do chemotherapy in a pet with cancer is a complicated decision with lots of uncertainties. First, many cancers are simply not responsive to chemotherapy at all. Many that are, are only responsive for a short period of time. In fact, in the majority of cases where we are use chemotherapy in pets, we are not curing their disease, but rather trying to prolong their quality of life. So it’s not always an easy call.

Second, there is the possibility for significant side effects. Chemo-therapy, simply, attacks rapidly dividing cells–—i.e., the cancer cells. But the cells in the intestinal tract and the bone marrow are also rapidly dividing, hence the chance for side effects such as vomiting, diarrhea, anemia, and a weakened immune system. However, chemotherapy protocols in dogs at least, are generally well-tolerated. They are designed to get as much control of the disease as possible, without making your pet miserably sick for extended periods of time. But tell that to the person whose dog spent the weekend in the emergency hospital because of fever and severe diarrhea a few days after their last chemo treatment.

Lastly, chemotherapy is expensive and becomes more expensive the longer they live. Not only are the drugs expensive, but they often have to be given in the hospital through IV catheters, and weekly blood tests are required to make sure the chemo is not wiping out the bone marrow.

Cost is a deal breaker for a lot of people, but nothing to be ashamed about. Who can argue with someone choosing to spend limited income on getting their child braces instead of trying to keep their 14-year-old dog going for another 6 months? These are tough decisions and take a lot of thought and understanding.

In the end, chemotherapy is not done commonly. But it’s worth a discussion if you find that your old companion has been diagnosed with cancer. For some folks, four to six months of happy mornings and nudged elbows are worth it.


  1. I am a senior in high school that is heavily interested in veterinary schooling. I am writting a paper on chemotherapy in animals. This paper requires an interview with someone within this field. If you could contact me asap it would be greatly appreciated.

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