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My dog has a new lump behind his knee. Should I worry about cancer?

Updated On September 23rd, 2025

My dog developed a lump behind his right knee. It's about the size of a quarter and it wasn't there yesterday. He is a three year old neutered blue heeler mix who has had no previous health problems. How likely is it to be lymphoma?

3 Answers

Most Helpful Answer

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Answered By Rebecca, DVM

Veterinarian

Published on August 22nd, 2017

I would recommend a vet visit. The vet can do a needle aspirate and take a look at the cells. While this may be a location for a lymph node it does not necessarily have to be lymphoma. Enlarged lymph nodes may be due to cancer, or inflammation or infection. Or it's possible it's not a lymph node and may be another type of mass or swelling. I recommend a vet visit to try to see what is swollen and why.

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    Answered By Laura Johnson VMD

    Veterinarian

    Published on

    Hi, thanks for using Petco Pet Education Center, formerly Petcoach! If it is the only lymph node enlarged probably unlikely to be lymphoma. There are many causes for lumps under the skin: it could be a fatty deposit, skin infection, a cyst or a benign growth. Since it is sudden it is not wrong to have your Vet take a look at the lump. I wish you the best of luck!

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    Answered By Dr. Elizabeth

    Veterinarian

    Published on August 30th, 2019

    Any lymphnode that remains enlarged should progress onto another diagnostic. This next step could be either aspirating the lymphnode and sending the sample to a histopathologist in a lab or being a little more aggressive and get a biopsy and then sending that out. I recommend to choose one of these as the next step since the node has been enlarged for 3 months. Regarding the other masses, pets can get many types of lumps and bumps. Most of these tumors will be benign but some will be malignant and you can't tell by looks. Here is a helpful link discussing the various types of skin masses in general: https://www.petcoach.co/article/lumps-and-bumps-on-your-pet/ If any of these masses are changing, I would also recommend to collect a sample and send it out to a pathologist as well. It's hard to know from the photo if that node looks enlarged or not, I generally need to compare the node to the other nodes via palpation. Have your vet double check the size of the node before aspiration. I hope this helps and please feel free to post any additional questions.

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