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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


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  1. Susie Hesseldenz on June 18, 2014 at 3:34 pm

    My dog had a fna of a deep mass underneath his arm pit that bleed internally. The results were sarcoma, suspected hemangiosarcoma. The oncologist suggested surgery. Ultra sound and X-rays showed no signs of metastasis. I wanted to find out if it was hermangiosarcoma so I could decide if I wanted to put my dog through surgery, since surgery doesn’t necessarily help with the outcome of hemangiosarcoma.The hospital performed a trucut biopsy. The surgeon said he took roughly 6 samples all around the tumor. The results read “Granulation tissue with hemorrhagic debris consistent with the edge of a hematoma.” Also, no evidence of neoplasia(cancer). In the comments section said they still do no rule out cancer. I am so confused! What would cause one biopsy to say cancer and the next say no cancer?

    • RaymondSte on December 7, 2017 at 12:26 am

      The sad, cold hard truth is veterinary medicine, much like human medicine, is not an exact science. The best you can hope for is an honest, highly experienced vet who is straight with you and hopefully one of the never ending tests reveal something solid. But you’re still left with a hard, cold decision based on the age of the pet, his condition/prognosis and what you can afford, not necessarily in that order. This is no comfort, I know and this is exactly why my wife and I refuse to have any more pets. If you can’t afford to pay for their care as they grow older it is terribly unfair to the animal and heartwrenching if you have have them killed when they might be able to be saved for a couple more years. Nope. Ain’t goin’ down that road no more. I’ll get a pet rock.

  2. Susan Kazara Harper on June 17, 2014 at 12:30 pm

    Hi Joanna,
    I understand the confusion, and you must have been worried and frightened, thinking for even a moment that amputation had not been required. Here’s the thing; aspirates are simply not a reliable method of diagnosis, and you’ll find that most oncologists will not even consider them. An actual biopsy of a portion of tissue is much more accurate. Oncology is a highly specialized subject, and when you realize that there are fewer than 500 veterinary oncologists in the USA, and a lot of them are in research facilities rather than vet clinics, one often doesn’t get to deal directly with an oncologist for their dog’s situation. The confirmation of the presence of cancer was consistent in both opinions however, and while I know you’re a bit distressed, and hoping for facts, the focus now can be simply taking care of your dog and moving on with recommended treatment. How is your girl doing after the surgery? Most dogs rebound quicker than we’d believe, and when the limb that was causing discomfort is not an issue any longer, they can get back to enjoying each day. So please don’t spend time worrying about the possibility of MCT. Learn the signs of course, ( and be vigilant but not anxious. Voice your concerns to your vet, and follow up with any recommended future checks. The job now is to fill your girl’s day with the best nutrition (The Dog Cancer Diet) to help keep her strong, follow the recommended veterinary treatment protocol, and please consider Apocaps as a first-choice nutraceutical to help keep her body’s cells firing in a healthy way. Also, have you seen the website It’s SO helpful. Please let go of the worry of what perhaps might have been, and focus on what is. Your girl needs you at the front line with her, as a happy guardian celebrating her every tail wag. All the best to you both!

  3. Susan Kazara Harper on June 15, 2014 at 3:37 pm

    Hello Shannon,

    Fine needle aspirates are not very accurate. A full removal with clean margins, and a biopsy is really the best way to tell just what you may be dealing with.

    Equally it is a big and possibly expensive decision to make. Trust your instincts. If you want to get a second opinion and even another quote for the cost of the surgery and biopsy then by all means do that. You are your dog’s champion, and I know you want the best for your boy. You have the benefit of a young, mixed breed dog (lab x beagle sounds gorgeous!) and that gives him good odds in this. You also caught these within a couple weeks of their appearance. Another great plus.

    I urge you not to ‘wait and see”. If these turn out to be nasty you will regret the wait. Early detection and action are your best bet. You may find that there is an vet oncologist near you. If you need help locating one, do call me on 808-568-3252 and I’ll help in any way I can. Please stay positive. We’re all rooting for you both.

  4. shannon on June 14, 2014 at 6:04 am

    Hi. I have a one yr old lab,/ beagle mix with a dime sized mass on the the side of his abdomen and a pea sized mass on his front leg that came up in the last 2 weeks. My vet said its an histeicytemia or a mast cell tumor and wanted me to do a complete biopsy removal that will be over $1200. He didnt even mention an fine needle aspiration. Both of the mass are round,hairless that sometimes looks red but then whitish on top. What does it sound like to you, or is a biopsy with anesthesia is necessary or should i go to another vet for a second opinon.

  5. Joanna on June 12, 2014 at 1:13 pm

    My dog had a very large tumor on her hind leg and the cytology report from the aspirate came back stating that it was a mast cell tumor. Because of the size and location, I was told that amputation was the only option and her leg was amputated 2 weeks ago today.

    The histology report came back and apparently it wasn’t a mast cell tumor but instead was a neurofibrosarcoma and was assured that even though it is a different kind of tumor, the treatment of amputation would have been the same.

    I am concerned by the fact that the reports can be different. Clearly, one of them is wrong and I don’t know how to process this for myself. When I asked the surgeon, he claims that he is 100% confident in the histology report and that cytology reports are often incorrect. However, if they cytology report is positive for mast cell, I’m concerned that I should be wary of mast cell that is perhaps somewhere else in here body.

    I understand that a cytology report can be inaccurate as far as detecting vs not detecting cancer cells but I don’t understand how they can be inaccurate as far as determining the TYPE of cancer cells. Aren’t the types of cancer determined by the size, shape, growth pattern, etc. of a particular cell? I just don’t understand why cytology would be positive for mast cell but the histology of the actual tumor shows no sign of mast cell but is NFS.

    I am very confused right now 🙁

  6. Susan Kazara Harper on May 27, 2014 at 11:37 pm

    Hi Kelsi,
    Here’s the thing.
    If you only have the lumps biopsied, it will still involve anesthetic and surgery for your boy. The small amount of tissue taken will be tested. If either come back suspicious, or confirmed cancerous, you may then decide to have another anesthetic and surgery to remove the lumps. Now you’re on two operations (along with the cost, the stress and the healing for your boy).
    If your vet goes in to remove the lumps (either or both) the tissue can then be thoroughly biopsied, and he or she will aim to get clean margins, i.e. taking all of the mass away if possible. By taking the entire mass it’s possible to biopsy several areas of the lumps… if there is cancer, the cancer cells may not be spread throughout the whole mass evenly, so checking several areas of a lump makes more sense from that point of view.
    So it’s really down to how you feel and what you decide, based on how you know your dog, what’s in your heart, and your vet’s professional opinion. If your boy is hale and hearty and eating, sleeping and pooping well, he may be a good candidate to sale through surgery. Your vet can help you gauge this, and listen to your gut.
    I hope this helps. You are the only one who can make these decisions, but you’re doing the right thing by reaching out for information. Breathe out any fear, check your facts and talk to your dog about it too. Good luck to you both!

  7. Kelsi on May 27, 2014 at 10:02 am

    Hi Dr. D

    I have an 8 year old yellow Labrador. He has developed a really hard mass near the base of his tail over the past 8 months. The size is about that of a baseball or softball. I had the FNA done about three months ago which was inconclusive. More recently it has gotten bigger. I made an appt with our local vet to have it removed, but now after reading these posts, I feel like I should just have it biopsied? Additionally, he’s had a rapidly, and I mean RAPIDLY, growing tumor over the past month pop up on the left side of his body.This tumor is kind of squishy. Please advise as to whether or not I should have both of them biopsied or removed.

    Thank you


  8. Jennifer on December 8, 2013 at 10:23 pm

    Can you help? I have a blue Great Dane who is 7 1/2 years old. I found a growth on the left side his neck about the size of a flat baseball. His vet did a fine-needle aspiration biopsy that came back inconclusive but did no other testing. Because of the location of the growth being so close to major arteries, throat, etc it needs to be removed…but is risky for all the same reasons. I’m not sure what to do? Should I get another opinion? What kinds of questions should I be asking?

    • Susan Kazara Harper on December 9, 2013 at 3:54 am

      Hi Jennifer, I know this is a worrying time, but hang in there. The throat is a delicate area, but you’re lucky that your big dog has a big throat. There is more room to work. If the fine needle aspirate was inconclusive, the next step is to get a biopsy by having a piece of the growth removed surgically. This will involve general anaesthesia. Because as you say it is advisable to have the lump removed anyway, it is worth considering whether to just have the lump totally removed and have it biopsied rather than having one surgery to tell you what it is, then another to remove it. The lump could be a fatty mass, an abscess, an infection, or a cancer. Is the lump interfering with your dog’s ability to eat, drink or be happy? These are all consideration for you as well. It’s up to you whether you get a second opinion, but if it sounds like your vet is reluctant to do any surgery, and you want to know what you’re dealing with, you can ask your vet if there is a surgeon you can go to who specializes in this type of soft tissue surgery. It’s not possible for every vet to have loads of experience in every department. So step 1 is to decide whether you want to move forward with this next stage of surgery to know what you’re dealing with. If the answer is no, ask your vet what treatment options, if any, are available now. If you want surgery, getting a specialist is a good move and will give you more confidence. Then it’s step 2, finding out what that lump really is. If you get confirmation of cancer, you’ll want to ask the type of cancer, and the stage/grade of the lump. This is all information to move forward, and there is much that can be done. But please don’t spend your energy worrying about a diagnosis you don’t have yet. One step at a time. Good luck and please give your dog a hug from me.

  9. Amy on June 7, 2013 at 6:20 pm

    I’m want your thoughts on the below:
    I went to a new veterinarian. I had asked this veterinarian to do a number of things, and one of them was to examine my 11 year old, canine companions’ growths on her chest. My canine is NOT obese; she is simply predisposed to tumors. My old veterinarian had aspirated these growths in years past with benign results. However, this veterinarian not only did NOT aspirate her growths, he didn’t even really feel her chest to examine all the growths. (My limited experience with him was that he would not listen to me…) I would appreciate your viewpoint on the above.

    • Susan Harper on July 1, 2013 at 8:49 am

      Hi Amy, Well done for being proactive about your dog’s health and asking for investigative check-ups. It’s frustrating to be met with a response that seems less than helpful. I know it’s been a few weeks since you wrote, and I apologize for the delay responding. I don’t know why you have gone to a new veterinarian… perhaps the previous vet no longer practices, or you’ve moved etc. However, you are your dog’s best friend and champion. If you are still struggling with this frustration, I can suggest two approaches. You could go back to this new vet and either when you make the appointment or while you’re in consultation with the vet explain that it is important to you to have these lumps checked as you have done in the past, and that you would appreciate him either taking the aspirations for you or referring you to a vet who will. Or, find another vet. You want to have a good partnership with your dog’s health care provider, so establishing that in these first appointments will help you both. Vets are truly animals lovers, but we can all have a bad communication day. I’m sure you’ll find this or another vet who will be happy to take care of your pup. Good luck. Susan form the Dog Cancer Support Team

  10. Jennifer on November 5, 2012 at 10:37 am

    I have a 3 year old Newfoundland who had a FNA done of a large mass on the side of his neck. It started out the size of a golfball and within 2 weeks it is now bigger than a grapefruit and seemingly growing every day. We started him on cortisone but the lump keeps getting bigger. My vet said it was most likely lymphoma but we’re awaiting the results of the FNA. Isn’t he too young to get this type of cancer? If it is cancer and growing this fast – how long should I expect him to live? He still eats, plays, runs etc.

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