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Understanding biopsy report.

Species: Dog
Breed: lab mix
Age: 2-5 years
Hi Dr. Marie,

I imagine you are getting sick of hearing from me. I'm sorry…

I emailed you earlier this week about a mass on my dog, Honey. The vet was sure it was a mast cell tumor, but then the needle aspirate said it was likely not a mast cell tumor, and he started her on antibiotics (Clavamox, 312.5 mg 2x/day) in case it was an infection instead.

She has been on the Clavamox since Wednesday night (7 doses). And the mass, which was very red, inflamed, and oozing a bit has now healed over and shrunk. However, in the past two days it really hasn't changed at all. It is now a small pink bump, about 0.5 cm (before it was probably about 1 cm).

It appears that any sign of infection is gone (I'm going to finish the full course of antibiotics or course) so I'm concerned about the next steps.

I was wondering if you could help me understand the cytology report :

--
Microscopic Description:
"Cellularity is low with a mixed inflammatory cell infiltrate admixed with a few sheets of mature sebaceous epithelial cells and a small amount of blood."

Comment:
"Cellularity slow and may not be fully representative." The sebaceous epithelial cells may be contaminants from the skin or may indicate a sebaceous epithelial proliferation (rule out sebaceous hyperplasia or a benign sebaceous adenoma or other adnexal tumor). The inflammation may be related to chronic trauma, infection, foreign body, neoplasia, etc. Correlate with clinical impression."
---

My main concern is that even though the bump has gotten smaller, when I take her out for walks it gets redder and a bit more inflamed for a time being (although it's not ulcerating or anything). I have read that mast cell tumors change size when they are aggravated. However, this is also in her armpit area, so it is impossible not to irritate that area when she walks. Is it possible it is something benign, just getting rubbed the wrong way?

I am supposed to call the vet on Monday to follow up on this. I am looking for some guidance on how to approach this. Do you think I am concerned unnecessarily? Is it likely to be something benign that had become inflamed, or is the fact that it is sticking around, despite antibiotics, a reason to have it removed? Like I said, it is quite small, but it has not gotten any smaller in the past few days…thank you for your time.


Online vet, Dr. Marie

Dr. Marie replied:

Hi. I'm glad to hear that Honey's mass has shrunk significantly and that the infection seems to be cleared up. Let's see if I can help explain the cytology report for you.

"Cellularity is low with a mixed inflammatory cell infiltrate admixed with a few sheets of mature sebaceous epithelial cells and a small amount of blood."

This means that there weren't a lot of cells on the slide. Usually, mast cell tumors will produce a decent number of cells for the pathologist to look at. The types of cells that the pathologist is seeing look like infammation as well as sebaceous epithelial cells which are basically skin cells and then some blood.

"Cellularity slow and may not be fully representative"

Did you mean "Cellularity is low?" "Slow" doesn't really make sense here. But low would mean that there weren't a lot of cells on the slide and as such we could be missing something. This is the case almost every time we do a fine needle aspirate. It's never as accurate as looking at the entire lump as a full biopsy.

"The sebaceous epithelial cells may be contaminants from the skin or may indicate a sebaceous epithelial proliferation (rule out sebaceous hyperplasia or a benign sebaceous adenoma or other adnexal tumor)"

Sebaceous cells are basically skin cells near glands on the skin that secrete material...kind of like sweat glands in people. There are some rare situations where when we see sebaceous cells on a slide it is not just skin cells but a more serious condition such as the three mentioned above. These are really uncommon and I really wouldn't be concerned about them at this point.

"The inflammation may be related to chronic trauma, infection, foreign body, neoplasia, etc. Correlate with clinical impression."

This is the pathologist's "cover your butt" statement. They're basically saying that they think that the lump is caused by inflammation but as there are many possible causes for inflammation, no one can say for sure what the cause is. The clinical view of the lump (i.e. the history of the dog and what the vet is seeing) can help in making this decision. The options that are given here include chronic trauma (i.e. something rubbing on this area consistently), infection, foreign body (i.e. there's a splinter or something in there), neoplasia (cancer). Any time there is a lump, cancer has to be a possibility. Given that the lump has decreased by half in a short time, I would guess that this is unlikely, but we can't rule it out completely.

It's true that mast cells can change from time to time, but I wouldn't expect a mast cell tumor to shrink so much so quickly with just antibiotics. Given that the lump is near her armpit it may be that she is just irritating it as she walks and that is why it is redder after exercise.

At this point, your vet will give you the best guidance. But, if this were my case I would likely be telling you to keep an eye on things. If the lump was still there in a few weeks or if you felt it was getting bigger then I'd likely remove it and send the lump away for a complete biopsy. I'm guessing it will be gone in another few weeks though.

Hope that helps! Dr. Marie.


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Disclaimer: Although Dr. Marie is a qualified veterinarian, the information found on this site is not meant to replace the advice of your own veterinarian. AskAVetQuestion.com and Dr. Marie do not accept any responsibility for any loss, damage, injury, death, or disease which may arise from reliance on information contained on this site. Do not use information found on this site for diagnosing or treating your pet. Anything you read here is for information only.

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Dr. MarieDr. Marie is a veterinarian who practices in a busy animal hospital in Ottawa, Ontario. She created Ask A Vet Question as a resource for good, accurate veterinary advice online. Dr. Marie treats dogs, cats, hamsters, guinea pigs, and rats. She has been a vet since 1999.

Is an online vet visit just as good as a trip to your veterinarian? No! But, many times, asking an online veterinarian a question can help save you money. While Dr. Marie can't officially diagnose your pet or prescribe medications, she can often advise you on whether a vet visit is necessary. You can also ask Dr. Marie for a second opinion on your pet's condition.