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Featuring Demian Dressler, DVM and Susan Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Carcinogenic Chemo Drugs

Updated: January 10th, 2019

One of the biggest ironies I have encountered are carcinogenic chemotherapy drugs.

Sound odd to you?  Well, I don’t blame you!  When I first found out about it I was shocked.    Medication used for fighting cancer actually increasing the odds for cancer later?

Now, before everyone gets reactionary, we have to temper this topic with the big picture.  Chemotherapy has helped a lot of dogs live longer lives with good life quality.  Let’s not forget that reality.

The problem is that this is an area of medicine where the treatments used can, at times, have real-life and quite severe side effects.  This is simply a reality of conventional cancer care and needs to be accepted as the current state of affairs.



I discuss how to lessen chemotherapy side effects in detail in The Dog Cancer Survival Guide if you are interested in this topic.

Take cyclophosphamide (Cytoxan), a common chemo drug used in dogs.  The truth is that this medication is a known human carcinogen, and the same was found in rodents. Here is some information on the topic.

Cisplatin is “reasonably anticipated to be a human carcinogen,” and is carcinogenic in lab rodents.

So what does one do with this information? How are we supposed to feel okay about the use of these drugs?

Well, the age of the dog has to be kept in mind. While nobody knows the exact timing of a possible cancer developing after exposure to these drugs, it likely takes a while.  Although I cannot give real data, a guess could be 3-5 years or more.

So it would make sense that in a young or middle aged dog, one might reach for different chemo drugs, especially if a normal life expectancy (without the cancer) would be more than 3-5 years after the cancer.  This is an uncommon situation.

These are very tough decisions as nobody has a crystal ball.  However, as your dog’s primary health care advocate, you should be advised of all the facts.  We don’t know whether a second cancer will develop, but we need to at least evaluate carefully.

All my best,

Dr D


Discover the Full Spectrum Approach to Dog Cancer

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  1. Tarun Grag on June 3, 2014 at 2:18 am

    Thank you for sharing your valuable information.this information very useful for online learners

    chemo drugs

  2. DCA Not Advised At This Time for Dog Cancer on April 25, 2012 at 7:54 pm

    […] (ouch!), which of course does not bode well for a cancer treatment.  Truth be told however several chemo drugs are carcinogenic and are being used right now widely. Very deeply ironic but true. We do the best we can in medicine […]

  3. Becky on February 23, 2010 at 7:35 am

    I’ve been reading through different blogs and found this one on Cytoxan, I have had an underlying fear that this may have caused the brain cancer in my Weimaraner. Five years ago my husband very suddenly became sick with Polyarteritis Nodosa, a rare auto-immune neurological disorder where his immune system attacked his arteries to his nerves and muscles, his arms and legs became numb and limp in 10 hours, and have taken 5 years to regrow. In order to shut down his immune system, he took high doses of Cytoxan daily for 3-1/2 years. During this time my dog, who is a certified therapy dog, would carefully lay next to him in bed, with the top of his head next to my husband’s mouth, my husband breathing on the very spot where my dog’s meningioma or meningeal carcinomatosis developed. They spent many, many hours every day like this. I wondered at the time if this would hurt our wonderful dog, but it was such a great comfort for my husband who was struggling for his life, I felt that if something happened to our dog he would have gladly given his life for his master. I will never discuss this with my husband or anyone else, except now you in a venue my husband won’t see, but I have to ask – could this have caused my dog’s brain tumor? It might be important to know if my husband has to go back on the Cytoxan someday.

  4. Lilly F on September 26, 2009 at 9:31 am

    More thoughts–it is weird it is just on the face–is this a contact dermatitis of some sort–is she laying on something irritating? Is it anxiety where she has developed a habit of doing this? Was the dog checked for one of the types of mange which I think is seen on the face first?? Good Luck