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Featuring Demian Dressler, DVM and Sue Ettinger, DVM, Dip. ACVIM (Oncology), authors of The Dog Cancer Survival Guide

Fine needle aspirates to diagnose dog cancer?

Updated: April 4th, 2019

Hi everyone,

I have been getting questions about the best way to gather info about growths in dogs.  So, let’s take a look at a common technique used to accomplish this…a fine needle aspirate.

First of all, a fine needle aspirate is not a biopsy.  A fine needle aspirate is a sample of the mass taken with a skinny little needle (meaning, not much to work with).  The vet will disinfect the surface of the site to be aspirated, often after clipping the hair, to prevent infection.  Next, a needle is introduced into the area of interest, and the plunger drawn back, creating a vacuum which draws cells into the hub of the needle.  These cells are then used to make a slide for the vet or a pathologist to look at for a diagnosis.

What is good about this technique?  Well, it takes about 2 minutes to do, and your dog gets to go home without sedation, anesthesia, or hospital stay.  Quick, easy, outpatient…nice. This is a good technique to diagnose TYPE of growth (in my hands about 75% of the time you get this info from the path lab after submitting the slide).

How about downsides? A fine needle aspirate cannot tell if the cancer cells have moved inside the body or spread into neighboring areas. There is a little inaccuracy in this technique as well. My experience is that about 1 out of 4 of these come back “inconclusive”, meaning there was not enough on the slide for the path folks to give a diagnosis.  Sometimes the vet will get a big sample, but the cells are just not the right kind to make a diagnosis (blood, connective tissue, etc.). Some tumors have a good cell yield, and others do not. Occasionally, we get an incorrect diagnosis with a fine needle aspirate.

Some dog tumors easily diagnosed with fine needle aspirates:


Mast Cell Tumors




Short story, this technique is a good, non-invasive, rough screen to get initial information.  Just keep in mind the limitations…it is not guaranteed and if there is any doubt in your vet’s mind, go for the real biopsy…coming up!


Dr Dressler


Leave a Comment

  1. Janis Krieger on October 26, 2022 at 2:19 am

    My vet feels my dog has a cancerous mass cell tumor, I understand they are one of the easiest to diagnose with a fine needle aspiration, yet He comes back and tells me there were cells all over the place. Then He wanted to send slide to a cytologist, but also told me He might not be able to diagnose. I dont’ want my 10 year old Boston to be cut open, what can I do?

  2. Maria on December 17, 2019 at 1:02 pm

    My dogs glands are swollen had a needle biopsy and came back inconclusive ? Should I assume she has cancer? Just so confused they told me that most likely it was but they don’t know for sure

    • Dog Cancer Vet Team on December 18, 2019 at 7:58 am

      Hello Maria,

      Thanks for writing and we’re sorry to hear that! In cases like this, it might be worth getting a second opinion either from another vet, or re-doing the needle aspirate 🙂 The sooner that you know what’s going on, the sooner you can create a treatment plan 🙂

  3. Clare Staplehurst-Miles on January 17, 2018 at 11:52 pm

    My dog has recently had a fna for a small lump found on his belly. The results are in today but i have been told i cant have the results as the vet is off work today. She will be back in tomorrow. We asked for another vet to tell us and they said they couldnt. Is there a reason for this? Now starting to worry.

  4. RaymondSte on November 9, 2017 at 11:03 pm

    I disagree with the statement about a fine needle aspirate not requiring sedation, anesthesia, etc. This may be true BUT the procedure on my dog’s paw hurt the hell out of him and the pain could not be controlled with Gabapentin AND Tramadol. This experience convinced me that if the toe has to be amputated we will permit it, with a whole lotta unease, BUT if the leg has to go…FORGET it. I’m not going to put a 13 year old pet through that awful experience of pain and then learning how to motivate on three legs.!!!

  5. Trisong Tibetan Terriers on June 6, 2016 at 3:52 pm

    So if the aspirate reveals malignancy, it is diagnostic and useful…regardless of whether the cancer has moved to other parts of the body. Inconclusive isn’t wrong…it is simply inconclusive, but the tool is still useful and a good first step especially when a young, apparently health dog is presented. My 18mth old beautifully coated, picture of exterior health TT was diagnosed in <12hrs by FNA with gastric/SI lymphoma. FNA of the lymph node was inconclusive. In the end it doesn't matter if the lymph node was negative or not, this cancer results in mortality.

  6. Chris Goodman on July 15, 2014 at 1:14 pm

    Please help!! Advise…I have a 2yr old neutered male Chihuahua/Jack Russell- He had what seemed to be allergy symptoms…watery eyes, swollen lids, licked his paws, and bum & a large lumpy abbess (? for lack of better description on his left cheek).

    First visit to vet: placed him on prednisone, antibiotics and 1/4 of a Benadryl.

    -little improvement- needle into abbess- found puss

    Second visit to vet: Shot of prednisone, more antibiotic (clavamox) – everything else as directed previously- oral prednisone & Benadryl. Added eye drops.

    -Improvement to eyes, still large lump thing on side of face- now finding additional lumps (m&m sized) on body…armpit, groin.

    Third visit (different vet): Another needle into now cherry sized lump on face, again found puss, thought it might be an infected salivary gland (??) . Showed vet additional smaller lumps, said “hmmm, watch them, I think they are fatty in nature”.. told me to stay the corse with the eye drops, Benadryl, stop prednisone and changed his antibiotic to Baytril.

    No change!! eyes still icky, lumpy, — I am SOOOO worried about this lil dog. Is there anyway for you to tell me the likelihood or not of it being cancer related?? My heart is heavy, and my dog is sick. He is eating great, pooping is normal and healthy. He is tired, but so am I on Benadryl!! Any thoughts would be so greatly appreciated!!

    I have appointment number 4 in two more days!

    • Susan Kazara Harper on July 17, 2014 at 2:20 pm

      Chris, This all came on suddenly and of course you are worried. You need to know what these lumps are, and you’ve already waited for some time while various meds were tried. “Wait and see” is no longer the best advice for lumps and bumps. If you aren’t happy with the response to your request, you have every right to get a second opinion, and it should probably be from a different veterinary practice. Please take photos of these lumps and their condition every couple of days, and place a coin like a dime or a quarter next to them for perspective. These photos will help any vet better understand. You can also ask your vet to refer you to a specialist. In the meantime, try to think whether your dog was exposed to any environmental changes – – pesticides on lawns or flower beds, nearby fields sprayed, a change to any chemicals within or around your home. Summertime is the worst for this type of thing, and our pets can often suffer for it. Get your information, insist on a referral or a specialist, and your pup will get relief that much sooner. Good luck!

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