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My dog has a leg bump. Is it benign if the FNA results are unclear?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed | Female | spayed | 9 years and 2 months old | 4 lbs

Precious has a bump since June on her inner leg. Only grown a little, doesnt bother it & isnt having any other problems. Does this mean its a good chance of being benign? The needle aspiration came back as something the vet couldnt read but it was something of the same cell & tightly packed. If there were mast cells she would have seen & knew that right? It will be removed & tested but im still so scared. Shes my best friend Also since the needle yesterday its oval shaped instead of round. Why?

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3 Answers

Most Helpful Answer

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Answered By Megan, DVM, CVA

Veterinarian

Published on April 8th, 2018

Poor Precious! I know you are worried about you! Good news is that most mast cell tumors are easily distinguished on an fine needle aspire (FNA). The chances of it being a mast cell tumor is less likely but not completely ruled out. Also, the fact that it hasn't grown much and the cells on the FNA were very similar in size and shape means it is likely benign. I think you are making the best decision to have it surgically removed and tested. Also, it is likely more oval due to some local inflammation secondary to the minor trauma a FNA causes. I hope this helps!

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    Answered By Laura Johnson VMD

    Veterinarian

    Published on April 8th, 2018

    Hi, thanks for using Petco Pet Education Center, formerly Petcoach! I think it is encouraging that the mass hasn't grown in almost a year. The cells all looking the same doesn't mean it is benign though. Since your Vet isn't comfortable reading the aspirate there is no way to know until the biopsy comes back. You could ask the Vet to send the slides out to help ease your worry until surgery. There are Mast Cells, specifically grade 1, that are essentially benign as removing them is curative and they have very small chance of growing back. I know you are very nervous but no one will know until the mass is removed and submitted for biopsy! Have a good weekend!

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    Answered By Dr. Leigh, DVM

    Veterinarian

    Published on April 8th, 2018

    I believe we have already answered questions relating to this bump. Do not worry as more than likely this is a benign mass but having it removed and biopsied would be the best way to confirm. A mass cell tumor can show up on FNA but it still could be.

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