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Lump under arm of puppy.

Species: Dog
Breed: Border Collie
Age: Less than 3 mon
We have a 10 week old puppy. He got his first set of vaccinations one week ago. Two days ago we noticed a lump under his left arm in his armpit. It is about the size of a pea and a little hard. We took him to the vet today because we thought perhaps it was a lymph node and he had an infection starting. He went to the vet this morning. His temperature was 38.9C (normal) and they aspirated the lump. When she came out she said they were able to aspirate and she said it had cells in it. She would be staining it and looking at it. Would probably send it to a colleague to look at and may send it to histology. She said it was on the connective tissue not muscle. She said it was hard to get because it moved as she tried to get it. My head jumps automatically to cancer. Is there anything else it can be or is more likely to be at his age and what impact does it have being on connective tissue rather than muscle?


Online vet, Dr. Marie

Dr. Marie replied:

Thanks for your question.

It would be extremely unlikely for a lump on a 10 week old puppy to be cancer. In 13 years of practice I can't say I have ever seen a puppy that young have a cancerous lump like you have described.

Is there any chance that any of Eclipse's vaccinations were given in that spot? It is a little bit of an unusual spot, but sometimes we do give injections on the side of the chest. It's possible his was a little further forward than normal (which can happen with a squirmy puppy).

If so, then this could be something called a vaccine granuloma. Vaccine granulomas almost always go away on their own but can take a month or two to do so. The textbooks tell us that they can sometimes become cancerous but it is very very rare for this to happen.

I have seen some unusual unexplained lumps on puppies that just go away on their own as well. Some of them could be perhaps scar tissue from a bite from a sibling or some other accident.

A lymph node really should have been easy to diagnose (as the cells all look like lymphocytes) and an infection/abscess should have been easy as well.

I think it is the right thing to do to send this sample to a pathologist just to be sure, but I'm guessing the diagnosis will be one of two things:

1. Vaccine granuloma - in which case we just wait and see and it should go down in a few days to weeks.

2. Diagnosis open - The pathologist may say, "Hmmm....I really don't know what this is but it's not likely to be anything to worry about."

Hopefully you will get some results soon but I will be absolutely shocked if this is cancer.

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.

Customer reply:

Thank you for the information :)

He had Lyme disease vaccine in his right leg and the Distemper, Parvo, etc. in his left leg.


Online vet, Dr. Marie

Dr. Marie replied:

If it was the back leg, then it's not likely to be a vaccine granuloma. But some random scar tissue is still possible.



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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.