A Day at the Vet: Dog Skin Cancer

My boxer Mojo.

As I woke up from a late Saturday afternoon nap and made my groggy way to the living room, my boxer Mojo greeted me as usual, with big slobbery kisses and those uncontrollably happy contortions that boxers are famous for.

But as I scratched behind Mojo’s ears and under his chin, I felt a strange hard lump right under his jawline, under his oversized boxer lips. The lump was very hard, about the size of a pea, raised above the skin and red in appearance. Rather scary, I might add.

Of course, this being Saturday evening, and non-emergency vet clinics closed until Monday morning, I did what I think most other bloggers and internet junkies would do – I rushed online. Through multiple forums, social media advice and (most probably under-credible) pet wellness sites, I came to the conclusion that Mojo had either an abscess, a benign histiocytoma, or an (unspoken) cancerous growth.

I waited rather excruciatingly until Monday morning to visit a veterinarian clinic in Durham NC (unfortunately I wasn’t at home with my familiar vet in Baton Rouge, LA).

“If you weren’t already aware, boxers are prone to a cancerous growth known as a mast cell tumor,” the vet said almost immediately after a brief examination of Mojo. “It’s good practice to investigate any bump or lump that shows up on a boxer.”

I’m trying to keep my spirits up, but this isn’t exactly good news. As it happens, mast cell tumors are the most common form of malignant skin cancer in dogs, and some breeds, including boxers, are predisposed to developing these tumors. The vet proceeds to stick a fine needle into the lump under Mojo’s chin, in order to confirm whether the lump is some type of infection or abnormal cell growth.

“Mast cells have a very definitive appearance,” the vet said. “Mast cells will stain bright purple in a cytology test.”

Staining of Mast Cells with Wright Stain, by Ed Uthman, Flickr.com

Staining of Mast Cells with Wright Stain, by Ed Uthman, Flickr.com

The vet was likely referring to Wright’s Stain or a variant thereof, a technique used to differentiate between particular cell types under a light microscope based on a colored stain. The methylene blue stain, for example, intensely stains the granules in mast cells that contain histamine, a chemical involved in immune responses and allergies (which, interestingly, boxers are also prone to).

After a few minutes of peering at cells from Mojo’s lump under the microscope, the vet returned to the room to inform me that she hadn’t seen any clear indication of intense staining, and therefore could not diagnose a mast cell tumor at that time. She said that, given the fact that Mojo is a young dog (only 2 years old) she was diagnosing the lump as histiocytoma, but that I should watch for it to grow, as that could be an indication of mast cell tumor.

A histiocytoma is a benign tumor, and often regresses without treatment in a few weeks to a month or so. Unlike the aggressive and malignant growth of mast cells, a histiocytoma is a growth of a different type of immune cell in the monocyte/macrophage line originating in bone marrow, the histiocyte. Boxers are ALSO prone to this type of tumor, especially young and otherwise healthy individuals.

Most commonly histiocytomas are found in young dogs and appear as a small, solitary, hairless lump… They are most commonly found on the head, neck, ears, and limbs, and are usually less than 2.5 cm in diameter. [Wiki]

Unfortunately, my boxer has a tumorous lump on his chin. Hopefully, this growth is benign. But again, unfortunately, I have to wait for a few weeks, monitoring the lump, in order to be completely sure that this diagnosed histiocytoma isn’t actually a more aggressive and malignant type of growth.

If you are a worry-wort dog owner like me, I feel your pain if your pup has ever been afflicted by a mysterious lump or bump. These growths, although common, can crop up overnight and create sleepless nights for us humans who love our pets. The good news is that, even if Mojo has a mast cell tumor, metastases (or spread of the cancerous mast cells) of this type of tumor are rare, and surgical excision of the tumor can lead to a positive prognosis.

If you know anything else about histiocytomas, mast cell tumors, or common boxer afflictions, please let me know! I’m also curious whether there is a connection between the hyperactive immune systems of boxers (resulting in allergies, etc.) and these tumors that are common to this breed.

I have allergies myself – could I be more prone to other inflammatory diseases and cancer?

9 Responses to “A Day at the Vet: Dog Skin Cancer”

  1. Emma Reply | Permalink

    Keep up the spirits! My weimaraner has had a big lump on his head since he was a pup. He is now 3 y and no major growth of lump. So there is hope with these lumps and bumps. I sometimes say his brain is in it because he is a crazy dog :)

  2. Michele Reply | Permalink

    Hi. I'm so sorry that Mojo has a lump. I understand how nerve wracking that can be. What did the vet say about removing the lump and doing a biopsy? Hopefully it is nothing serious. However, if it is a mast cell tumor, the best results are when it is surgically removed when the tumor is in an early stage. Our yellow lab, Rosie, had a mast cell tumor. She is cancer-free now but it was a scary time for awhile. I documented her experience on her blog http://rosiesroad.wordpress.com/.

  3. Paige Brown Jarreau Reply | Permalink

    Hi Michele! I am actually still waiting, to see if the lump is going down at all. It has been a week or so, and the lump doesn't seem to be getting any bigger at least... do you know if it is normal for a histiocytoma to itch my pet, and bleed if scratched?

    Thank you for the info!

  4. Anne Reply | Permalink


    Thank you for your post.

    I just want to encourage you because a few months ago, I was still in the dark about these malignant tumors and how they operate. My dog was diagnosed with a mast cell tumor, it kept on growing until it reached 2 inches.

    I found the real culprit and I changed her diet, In less than 4 weeks, the 2 inches mast cell tumor shrunk to 0.8 inches and in less than 5 weeks, the mass inside the tumor completely disappeared. Two months later, the tumor is gone.

    I'll be more than happy to send you the information and send you the diet that I came up with that reversed this 2 inches malignant tumor. Check my link:


    Thank you.

    • Paige Brown Jarreau Reply | Permalink

      Thanks Anne. It sounds like if your pet had what was diagnosed as a mast cell tumor that subsequently went away with a change it diet, it was probably a histiocytoma instead of a mast cell tumor. They could look very much alike.

      Mojo's tumor actually gradually grew smaller and is now no longer visible, so I am assuming it was a benign histiocytoma as the vet suspected.


  5. Diana Reply | Permalink

    Glad to hear your dog's lump went away. I first noticed a small, pea-sized lump on the front shoulder of my boxer when he was maybe 6 years old. I never knew his exact age because he was a rescue that was just running wild throughout the neighborhood for several days before I took him in. The vet and I kept an eye on it for a couple of years, and there was no change. Then when he was 8 I was rubbing his belly and felt a lump about the size of a small grape. While sitting in the vet's waiting room I found 2 more small (bb size) lumps, one by his tail and one on a back leg. Biopsy showed they were mast cell tumors, so I had all 4 removed. Surgery was tricky, because I mentioned that I suspected a heart problem, because even though he was very hyper, he'd also tire out very quickly. He could barely go for an easy, 1/4 mile walk! A sonogram showed he had boxer cardiomyopathy, another common boxer affliction. Anyway, surgery went well, but then 6 months later I noticed he had a sore on his lip that looked like he'd bitten his lip. This turned out to be melanoma, and surgery would have been very invasive. With his bad heart, I knew he'd never survive that, so I finally had to have him put to sleep.

    Rowdy was my third boxer, and all three lived to 9 years old. Boxers seem so strong, but they are really cursed with a lot of health issues. My first one had a huge mass in her stomach, my second one had a massive heart attack, and poor Rowdy had cancers AND heart issues! I love boxers, but I don't think I will get another one because their lives are too short in most cases. Good luck with yours! There was another one on my street that lived well into her teens, so it's not all bad. Just my bad luck, I guess.

  6. kay edwards Reply | Permalink

    My boxer has a tumor that has grown from small to about 4 inches in two months, my Vet says she is too old to remove it, she is 9 yrs. old . I could just die . The tumor is 2 inches high 4 inches across, and 10 inches around. How can I help her ? She plays like a young pup, and has a beautiful soul. What can I do, how long does she have? I feel so sick inside. She acts like its nothing, is she in pain? What is the next step, will the tumor burst and she bleed to death? Please any info would be appreciated. She is my family. Thank You! Miss Kay

  7. Cheryl Heckel Reply | Permalink

    Oh my goodness Kay, did you get a second opinion??

  8. Joanne Johnson Reply | Permalink

    I stumbled upon your blog, after finding that my 9.5 year old, female boxer had a cancerous tumor. (the vet removed it, it was between the skin on her eyelid). She has another lump on her back the size of a peanut, that has been there for a while; we're planning on having it removed. What caught my attention is that my dog "Maggie" looks almost exactly like Mojo. I saw that the other replies are a little old, I hope Mojo outcome was good. I'm trying to be logical about Maggie's prognosis, dogs don't outlive their humans, but they become as important to you as your children.

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