The 'Uncommon' Side Effects of Cancer Treatment

Published Apr. 10, 2013

During chemo appointments, I always catch up with owners to find out how things have been going since the last time I saw their pet. Since more than 75 percent of our patients won’t have anything happen to them after a treatment, I’m usually just checking in to confirm all is going well.

For about 20 percent of patients, there are mild side effects from chemotherapy — nausea, vomiting, diarrhea, decreased appetite, lethargy, etc. We usually hear about these events prior to a pet’s appointment as most owners keep us up to date (sometimes up to the minute…) about what's going on at home. We are all very comfortable explaining why the side effects can happen and what can be done to prevent them in the future.

Sometimes an owner’s observations stump me, and I'm at a total loss to explain what they are witnessing. It seems there are some potential “side effects” from chemotherapy I never learned during my residency. Perhaps some examples would clarify what I mean:

Me: Hi Mr. and Mrs. Smith! So good to see you! I’ve taken a look at Fido, and his exam and blood work are both completely normal! The technician said he didn’t have any reaction to his treatment last week. That’s great!

Mrs. Smith: Yes, we really haven’t noticed any side effects from his treatment, and he still has a ton of energy. So much so that we think, well lately he’s just been extra, I don’t know exactly how to put it, but maybe “frisky” would be the right word?

Mr. Smith: Frisky? Is that what you’re going to call it?

(I notice Mrs. Smith’s cheeks have turned an interesting shade of crimson and her eyes are not making contact with mine anymore.)

Mrs. Smith: Well it’s really not a big deal, and we’re really happy with how Fido is doing!

Mr. Smith: Not a big deal! It’s not your pants leg he won’t stop latching on to!

After a few stunned moments of silence, suddenly it becomes clear to me that a diagnosis of cancer and a course of chemotherapy caused a dramatic rise in Fido’s libido, or at least according to his owners it did. As I certainly never learned about this side effect during my training, I had no response other than, “Maybe we should look into finding him a girlfriend?”

Another one of my favorite “complaints” came from the owner of a cat diagnosed with lymphoma, who noted with complete seriousness that her cat “never blinked” since starting treatment.

“I can just stare at her and she will stare back at me and never blink!” she wailed, thoroughly upset and completely expecting me to explain her observation. I sat speechless. I pictured my own cats and thought, “I seriously cannot think of when I’ve seen any of them blink before! Do cats really blink? Did I miss the day in vet school when we learned the appropriate blink rate per minute for a cat?” Nothing I offered would console this owner, and I left the room feeling like a bit of a failure.

“Ben’s” owner once told me he thought his dog was becoming “nostalgic” from chemo treatments. This conjured up images in my head of his beloved Ben sitting at home in a high-backed chair near the fireplace, winsomely peering through photo albums of his “life before diagnosis.” Would he have a pipe in his mouth and a faraway look in his eyes? It took a full three minutes, and a lot of awkward silence, before I somehow realized that he meant “lethargic” instead of “nostalgic.” I was able to assure Ben’s owner that this was not something life threatening at that time.

Many owners note their dog will bark less after starting chemo, and equally as many note their dog will bark more. Dogs sleep “harder” and cats “sleep more.” Dogs will “pant more, but only at night” and cats will “yowl more, but only at night,” and I’m left wondering how it is that owners know what their pet is doing more of at night, when they are not home during the day because they are at work?

I don’t mean to downplay owners’ fears for their pets. There are definitely legitimate concerns to watch for while a pet is undergoing treatment, and it is also important to watch for signs of disease progression. I also recognize that pets are likely to experience some of the more nebulous side effects from treatment, just as people do, but are unable to communicate them to us in a way we can understand.

However, I secretly find it just a tiny bit amusing knowing that many of the signs they describe are likely because they are simply watching their pets so much more closely now that they’ve been diagnosed with cancer. All the strange and bizarre habits and behaviors that are now becoming so much more noticeable are the same behaviors they had their entire lives; they are just part of what make pets such wonderful parts of our lives.

In other words, if you stopped staring at your cat, maybe she would stop staring right back at you and blink once in a while. I know. I’ve tried it myself.