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

The Oncologist’s Perspective on Chemotherapy and Low White Blood Cell Counts: Part 1

Updated: January 28th, 2020


Chemotherapy and Low White Blood Cell Counts: how important are these low counts? How do they impact your dog’s cancer treatments?

In recent posts, I discussed gastrointestinal, or GI, side effects resulting from canine chemotherapy treatment. In the next few articles, I’m going to go over chemotherapy and low white blood cell counts, specifically, bone marrow suppression, in dogs. There’s a lot of information to share, so let’s get going!

Reminder: Chemotherapy Kills Rapidly Dividing Cells

The reason we use chemotherapy in dog cancer treatments is chemo agents target and kill rapidly dividing cells, and cancer cells divide rapidly. Unfortunately, some normal cells in the body also divide rapidly, which means they may also suffer damage.

Which cells beside cancer cells divide quickly? The most commonly affected cells are those in the GI tract, like the lining of the mouth, esophagus, stomach, and intestines. The white blood cells in the bone marrow are also very commonly affected. Interestingly, a common side effect of chemotherapy in humans is hair loss, but that doesn’t usually happen in dogs. It can happen, but it doesn’t in always.

So let’s look at white blood cells in more detail.

White Blood Cells

Bone marrow, that spongy material at the core of bones, produces three types of blood cells: red blood cells, white blood cells, and platelets.

These cells are being born in the bone marrow, which is why they are rapidly dividing and likely to be affected by chemotherapy. That said, of all these cells, the white blood cells being born in the marrow are the most affected. (Already-developed white blood cells that are actively circulating in the bloodstream are not dividing, so they are not affected.)

Chemotherapy and Low White Blood Cell Counts

When chemotherapy agents destroy cancer cells, they can also destroy these rapidly dividing white blood cells in the bone marrow. But you might not even be able to tell!

Unlike GI side effects, which can show up as unmistakable diarrhea, vomiting, and nausea, a low white blood cell count is undetectable by behavior. Your dog won’t act like anything is wrong.

The only way to know if the white blood cell counts have been affected is by getting a blood test. This is why most oncologists, including myself, will test your dog’s blood before and after treatments.

What We’re Looking For

There are five types of white blood cells, and their numbers make up the total white blood cell count. Each of these white blood cells has a different function in the body. But when it comes to chemo treatments, we’re really only worried about one type of white blood cell: the neutrophil.

When we oncologists talk about the “white blood cell” we are almost always really referring to the neutrophil.  Neutrophils fight infections in the body, so they are very important for overall health. If the neutrophil count is low, your dog is immuno-compromised and at risk for an infection.

A decreased neutrophil count, called neutropenia, is one of the signs we monitor to decide about dosing decisions. We decide how much to give of most drugs by looking at how low the neutrophil goes after treatment. If the dose from the last treatment caused a big plunge in your dog’s neutrophil numbers, we will change the dose to a lower one or skip that agent in the future.

This is a really important thing for you to understand: there is no “one dose” that we always use for every cancer case. Your dog’s own response to the treatment helps us decide how to treat next!

We are constantly balancing. We want to give an effective dose of chemo, AND we don’t want the white blood cell (neutrophil) count to get too low.  That’s the balance of chemotherapy.

It’s important to understand that this test, the white blood cell count, is the main thing we use to find your dog’s limit for chemo treatments. The technical way to say this is that neutrophils are the “dose-limiting toxicity” for most chemotherapy drugs.

What’s Next

In the next article, I will discuss how and when I monitor the white blood cell count during treatment. I will also cover ways to minimize the chance of infections in dogs getting chemotherapy.

Until then, be sure to check out more about chemotherapy and its side effects in the Dog Cancer Survival Guide.

All my best,

Dr. Sue, Cancer Vet

Also, See:

The Oncologist’s Perspective on Chemotherapy and Low White Blood Cell Counts: Part 2

The Oncologist’s Perspective on Chemotherapy and Low White Blood Cell Counts: Part 3

Leave a Comment

  1. Rachelle Harris on July 28, 2021 at 12:48 am

    Thanks for the great info on how the WBC count and neutrophils are so peripheral to the dogs wellbeing through their cancer treatment. We have a dog currently living with osteosarcoma (appendicular) – he had an amputation of his hindleg. Anyway, he has had chemotherapy – he had some neutropenia beforehand – and his white blood cell count and his neutropenia have dropped yet again. Even lower than last week and he has not had chemo for almost a month. Because he has lytic lesions on his spine and pelvis we are aware his treatment is palliative. However we are currently addressing with our pet oncologist what other treatment modalities might be appropriate for him considering the stage of his illness.

  2. Betty Jones on August 19, 2019 at 12:40 pm

    I would like to print out this article. How can I? There is no print icon.

    • Dog Cancer Vet Team on August 20, 2019 at 6:50 am

      Hey Betty,

      Thanks for writing! If you’d like to print the article, just go to the bottom of the page and you’ll see four sharing icons– one will be the print button! 🙂

  3. Kimberly on February 12, 2012 at 11:57 am

    My dog was diagnosed with lymphoma two weeks ago. He is on a regimen of leukeran alternating with prednisone. He seems to be doing well with it. You would never know he was sick. I took him to my VCA Vet the morning after I found his swollen lymph nodes. All blood work showed all blood counts were within normal range, and all his organs seemed to be functioning properly, meaning there were no elevations in kidney enzymes, etc. I started him on a product called K9 immunity plus from Aloha Medicinals. It is supposed to be an immune modulating compound they use on humans as well with good success. I did this with approval from my VCA vet. My question is, is there any other diagnosis there could be aside from lymphoma? They did cytology on the fluid they pulled from 6 samples of 2 lymph nodes. Showed immature leukocytes. My dog also has had bladder stones (calcium oxalate) that has been controlled for 3 years on Royal Canin Urinary SO. I am worried this food isn’t going to give him the nutrition he needs to fight his cancer, but I am afraid of giving him new stones if I give him something different. What can I do to ensure proper nutrition for him without harming him as well? I guess I was wondering if there was anything else that could be causing the immature leukocytes that might be something other than lymphoma. He is showing no signs of illness other than the swollen lymph nodes. They responded to the pred and leukeran in like 3- 4 days. They are almost undetectable now. I guess that is a good sign! Any information you could give me would be great. My Jug Nubby will be 5 tomorrow. Thank You!


  4. Mark on January 6, 2012 at 9:08 am

    So, if a dog’s neutrophils are within the acceptable range, even the upper end, would you say they are not immune-compromised? Or are there other factors to look at?

    • Dr. Susan Ettinger on January 15, 2012 at 10:49 am

      The neutrophils are just one cell of the immune system, and in general they are the infection fighting cells against bacteria and are also involved in inflammation. But they are not the only cells that work to keep us and our dogs healthy! For example there are lymphocytes – some are involved in fighting viruses, some are part of humoral immunity (antibodies), and some are part of what’s called cell-mediated immunity. To answer your question, you can have adequate neutrophils and part of the immune system can still be compromised. But this is a simplification of the very complex immune system.
      Hope that helps, Dr E.

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