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

Can Needle Biopsy Spread Cancer?

Updated: July 7th, 2021


Can needle biopsy or fine needle aspirates spread cancer? As always when it comes to dog cancer, there is no “one right answer.” Dr. Dressler, DVM goes over the facts.

Sometimes readers ask “can needle biopsy spread cancer?”

This is a reasonable question. After all, when we stick a tiny needle into a mass and suck up a sample of whatever is inside, we are literally putting a hole in that tumor. It’s entirely logical to wonder if that doesn’t allow what’s inside to spill out.

So when we do a needle biopsy or even a fine needle aspirate — are we spreading cancer?

Like all things medical, the answer is not simple. There are always many factors to take into account.

Fine Needle Aspirates and Biopsies

When we perform a fine needle aspirate or a needle biopsy, we insert a needle into the lump and aspirate (suck) a sample of tissue out. The sample is collected in a little vial attached to the needle, which we examine later under a microscope.

After we have our sample, we remove the needle, which, of course, leaves a tiny tract (tunnel) in the skin and lump.

So: do cancer cells move out of the hole we made with the needle and implant themselves along that tract?

Maybe, but not most of the time. Let’s take a look.

Tumors On or Under the Skin: Low Likelihood

If the tumor is on the skin or just underneath it, the likelihood that we will spread cells along that tract is really low. The tract just won’t be that long.

So, for tumors under the skin, or in the skin, the benefit of a solid diagnosis far outweighs cancer spread risk.

For these tumors, fine needle aspirate or needle biopsy is almost always a good idea.

Tumors Filled with Fluid: Higher Likelihood

So what about internal tumors?

Many tumors in the abdominal cavity (belly) are filled with fluid. They aren’t solid. The same is true for pericardium (heart sac) tumors.

In the case of tumors filled with fluid, it’s a good idea to be very cautious that the growths do not leak fluid with cancer cells through the tract.

Does this happen every time? Of course not!

In fact, it’s pretty rare. Also, there are ways to avoid it.

Your vet will be able to tell if a mass is filled with fluid by looking at the ultrasound images.

If your dog DOES have a fluid-filled mass, you could reasonably assert that you want to avoid a fine needle aspirate or a needle biopsy.

However, most veterinarians would be able to do one successfully.

I think it’s reasonable to be concerned, and I would tell your vet your concern.

And then, I would trust their judgment about whether they are capable of doing the procedure in your dog’s specific case.

Believe me, just mentioning your worry will ensure they take even more care than they usually do.

Solid Tumors: Low Likelihood

For solid tumors within the body, there is very little risk of spread along the needle tract.

So, if a mass looks solid on imaging, it’s almost always smart to get a specimen for fine needle aspirate or a needle biopsy if warranted.

Note:  There is one report of a lung tumor that spread along the needle tract in the dog, but this is only a single report, and thus we need more data before suggesting we avoid fine needle aspirate for lung tumors or solid tumors in the chest cavity.

That’s why, at this time, I am comfortable suggesting that all solid tumors are good candidates for fine needle aspirate or needle biopsy.

The only exception to this rule is if the mass is in the urinary tract.

Urinary Tract Tumors: Higher Likelihood

Growths of the urinary tract, which includes the bladder, urethra, and prostate, are most often transitional cell carcinomas.  These specific tumors have reports of cancer spread along the needle tract of a fine needle aspirate.

Now, again, your dog might be fine even if you do have an aspirate or biopsy of these tumors.

But if you are concerned, avoiding these procedures is reasonable.

After all, you can also test these tumors using a catheter to collect the specimen as a first step. Discuss this with your veterinarian.

Alternatives to Needle Aspirate or Needle Biopsy

Sometimes a diagnosis can be reached by taking a larger piece of tissue for biopsy. Instead of using a needle, other tools can be used to take a larger amount of tumor to examine.

Biopsies Do Not Cause Metastasis

What we’ve been talking about up until now is “local” spread of cancer, along the needle tract. Some folks also worry that fine needle aspirate or needle biopsies can also cause metastasis or distant spread.

At this time, we don’t have enough data to suggest that doing surgical biopsies in dogs causes distant spread of cancers.

This could change over time as more information comes in. There are a couple of tumors in other species where biopsy does (very slightly) increase the odds of spread.

All that said, in general, fine needle aspirates, needle biopsies, and biopsies are very safe.

For more general information about this topic, this abstract has some good data.

In the end, the scale tips most definitely in the direction of the biopsy.


Dr D

Further Reading

Klopfleisch R, Sperling C, Kershaw O, Gruber AD. Does the taking of biopsies affect the metastatic potential of tumours? A systematic review of reports on veterinary and human cases and animal models. Vet J. 2011;190(2):e31-e42. doi:10.1016/j.tvjl.2011.04.010

Nyland TG, Wallack ST, Wisner ER. Needle-tract implantation following us-guided fine-needle aspiration biopsy of transitional cell carcinoma of the bladder, urethra, and prostate. Vet Radiol Ultrasound. 2002;43(1):50-53. doi:10.1111/j.1740-8261.2002.tb00443.x

Tyagi R, Dey P. Needle tract seeding: an avoidable complication. Diagn Cytopathol. 2014;42(7):636-640. doi:10.1002/dc.23137

Minaga K, Takenaka M, Katanuma A, Kitano M, Yamashita Y, Kamata K, Yamao K, Watanabe T, Maguchi H, Kudo M: Needle Tract Seeding: An Overlooked Rare Complication of Endoscopic Ultrasound-Guided Fine-Needle Aspiration. Oncology 2017;93(suppl 1):107-112. doi: 10.1159/000481235

Leave a Comment

  1. Tammie on July 9, 2021 at 9:48 am

    What if the dog has a closed MCT and opens up after the biopsy and the dog licks it? Can the cancer go to the stomach?

    • Molly Jacobson on July 9, 2021 at 9:51 am

      Hi Tammie, that’s a really interesting question. I’d like to think that the acids in the stomach would destroy the tumor cells (if any were “eaten”). I have never heard of this happening, but that doesn’t mean it is impossible. In general, if you can keep your dog from licking a tumor, that’s obviously best. <3

  2. Bon on July 8, 2021 at 10:12 pm

    My Boys tumor need aspirate turned little blood scab. He then licked it opened scab and it became a nightmare towards the end green bacteria on it and him and I trying like crazy to keep it covered and clean as it became a huge baseball size open tumor with hole , see insides. From a mosquito like bite bump. And I was not warned could happen. Though him and I did a great job keeping covered and clean holding on till they could get us in in Pandemic for surgery. And acually took longer because he originally was having surgery at a Vets already beginning sedation and Surgeon thats a floater for local Vets decides on phone to try a skin graph from across his back! I said hell no! And went pulled him out. Then they final got him in at the Hospital Vets and that female Surgeon did how I wanted, cut it out and a nice nip and tuck! April? 2019 till now, great! Yet he has now a first size tumorin pelvis we are trying to make a treatment plan for ad this time I dont think surgery a good idea? It all started with anal glad cancer and that was the first surgery.

  3. P van Zyl on May 3, 2020 at 1:20 pm

    Hi Dr Dressler
    I urgently need your view on what I can do to help my doggy,, Herewith the case details,,, I saw your 2016 request for dogs with nose cancer to be tested at your facility.

    Hi I am from South Africa,,, my Eva is a border collie and presented with unilateral intermittent nose bleed,,
    I did not worry as I thought my other dog bit her, I also found my sliding door out of its rails and thought she bumoed her head,, or maybe an allergy.
    She had qyite a lot of basys systs that I could pop,, then found a small redish wartlike growth about 3-4mm in diameter on her head,, i scratched it with a pimple blade and next day she presented with a lump between eyes towards left eye on same side as nose bleed,,, Complete blood tests were done nothing to be alarmed of,, then they advised ct, because of bleeding and lump, but I missed the mail and then it was lock down,, now I took her to different, also a specialist vet, that was open, i asked for an xray sonar and aspiration and test for bacterial and fungus with an antibiotic developed,,, now he came back and say it is cancer and her glands are swolen, and cancer might have spread( could glands be because of lypoma aspiration 3 weeks ago at 1st vet specialist?”no glands before )  Eva is a very healthy active dog, 9yrs old, herding my other female border collie all the time.
    I cannot believe it has come to this,,, the doctor stopped the testing for bacterial and fungal as he said it is not any of that,, he went home but I phoned his assistant to tell the lab to continue testing, as I want to give her the benefit,,, i forgot to ask them to test for MRSA as well,,, only for Aspergillus fungus,,,i have read that often a fungus is misjudged for cancer,,
    My son had  Mrsa and i thought about that,,, as I have cut the skin and  the pimple blade was not sterilised,,
    Please, i need your view of this I can send photos,, also If i press on the lump then the pus bloody pink colour, drain through the nostril,,, and lump goes  away completely flat, but fill quickly again in half a day,,, the bone felt eroded under the skin where i pressed, not the same as other side of head, lump is centre near left eye,,, and dr said the xray showed bone eroding as well, the first specialist vet would not hear about an xray only wanted to do a ct scan. Can a ct still show more detail?

    Please your view is very important although I am so far away.
    She did have abtibiotics early on but it did not help, the lump got slightly bigger after that, and after she went for aspirate yesterday dr said he scratched on near the bone and took fluid from there(no tissue) ,,,now it is oozing out of the aspirate hole,,, but he did not give her anti inflamatories and lump is soo hot, also was very swolen could not even see her one eye,, swelling has subsided a little bit by now. Can surgery removal and radiation help? The doctor that did the aspiration wont operate, also that  the radiation does not allow for substantial time and that she could loose her eyesight.
    Eva is very special, most clever border/kelpie,, her sister is a drug sniffer dog on SA airlines, she is part of litter from our farm Kelpie mother and my sons Border Collie males, best sheep herding qualities. Just a bit of back ground.

    Will appreciate your inputs at your earliest.
    Photo after aspiration and following day. Swelling better, but lump still big, I am also waiting for pathology result from nose draining fluid swap before the aspiration at the normal vet.
    Please  advise urgently.

    Thank you
    Kind regards

  4. Chris Rynkiewicz on August 8, 2019 at 10:02 am

    Can a biopsy ever be wrong? My dog had a needle biopsy done of his shoulder & it came back chondrosarcoma. He was given a good prognosis with amputation, so we did the surgery. Overall health besides the cancer was excellent; he is a 10 year old neutered cocker spaniel. Now he started limping 1 week post-op and they tell me the limb came back as osteosarcoma instead of chondrosarcoma. The cancer is now in his opposite hip. He can barely walk and now they’ve mentioned palliative radiation. We’re devastated.

    • Dog Cancer Vet Team on August 9, 2019 at 7:06 am

      Hello Chris,

      Thanks for writing and we’re so sorry to hear about your boy 🙁 Your question is actually pretty common, and Dr. D wrote a pretty amazing article called, “Can a Dog Cancer Diagnosis can be Wrong?” that you may find helpful. There are also a number of really great articles on osteosarcoma that you may find helpful as well. Some of the articles touch on chemo, radiation, amputation, pain, and life-quality, to name a few.

      We understand how heartbreaking it is when you find out your dog has cancer. In Chapter 2 of the Dog Cancer Survival Guide, Dr. D writes that managing your emotions is critical when deciding upon a treatment plan for your dog. So take a deep breath, read over some of the information that you can find here, and go from there.

      We hope this helps.

      Thinking of you both <3

  5. Mya Gifford on April 12, 2019 at 6:35 pm

    So I’m in need of any and all advice please! I have an 11 year old pit-mix. About a week ago he developed a lump on his back right between his shoulder blades. I’m this past week it has grown tremendously, I would say it’s now the size of a baseball now. It’s hard as a rock and seems to be painless to him. Now, within the same week or so he has also developed maybe 5 or 6 smaller lumps elsewhere, all hard and painless. I’m on need of advice! Does anyone know what might be going on with my dog??

    • Molly Jacobson on April 12, 2019 at 8:35 pm

      Hi Mya, thanks for your comment. Please take your boy to your vet ASAP and get those lumps checked out. Anything that comes on that hard and fast is concerning. Here’s a good post to know when to get a lump checked: As Dr. Ettinger points out, any lump that is 1 centimeter or larger and/or has been there for one month or more should get checked out. In your boy’s case, he’s definitely 1 centimeter or larger! Get those lumps checked out right away, and we’re all pulling for you.

  6. Susan Kazara Harper on March 15, 2015 at 3:18 pm

    It’s often difficult to get tissue into the needle when aspirating. The material inside a lump can be liquid or lumpy itself, so sometimes multiples tries occur. The vet will be doing everything possible to get a good sample of tissue. Is this lump somewhere that it can be taken out surgically? A needle aspirate can possibly tell you what’s inside the lump, but if what’s inside is not benign you’re looking at surgery anyway. The best, ultimate treatment for cancer if it is cancer is to cut it out if at all possible, with wide margins to try to get every cell. If the lump is around the nipple it might be very possible to do this. Ask your vet, and get referred to an oncologist if it’s possible. It’s always best to have an expert in any field. Good luck to you both.

  7. ww on June 5, 2013 at 4:51 am

    We just had a FNA done on a mammary tumor about 2 months ago, and now its larger and also irregular, the vet had to inject multiple times with the same needle to try and get a sample to squirt onto the slide for lab analysis.
    They said that the results came back negative, assuming there was enough sample material on the slide.
    Oddly, the shape of the tumor now, like a “W” reminds me of the multiple stabs of the needle.
    Only time will tell if we made a grave mistake for our 7 year old.

  8. Mike S. on August 31, 2012 at 11:32 am

    Eli, our golden retriever (almost 8 years old), was a really happy dog, who in about April 2012 started having some constipation and straining when defecating. We had taken him to the vet at the time, who put him on some antibiotics at the time. It slightly improved, but he started up again in beginning of June 2012 with the same thing, and took him to the vet again, who looked at the stool, and saw that there was some hair, and they thought that was causing the constipation, and to give him some fiber, which we had done, but with no real improvement.

    Then, all of a sudden, one day, he couldn’t go pee, and had a sort of a deep grunt, which we knew was not normal, and rushed him to the vet yet again. We had also noticed some inflammation near his penis (they said it was adema). This was around July 25, 2012, and they did several x-rays, followed by an ultrasound, and suspected a prostatic carcinoma (as they saw some mineralization in the prostate). They started him on Rimadyl right away, as they didn’t have piroxicam readily available. A few days later, we say the oncologist and he did a fine needle aspirate of the prostate with ultrasound guidance. He was diagnosed with TCC of the prostate the next day around August 1, 2012. About that same day, we started him on piroxicam (of course NOT along with Rimadyl), but the adema never really got better.

    He was on piroxicam for about 2 weeks, and we had our first chemo session scheduled soon thereafter. However, a few days before we even started chemo, his back right leg started swelling up pretty bad, and we had to take him into the vet the day before the chemo session, as it just kept getting more swollen. The doctor did another ultrasound, and saw that the TCC had spread to the lymph nodes (who knows where else).

    They did the chemo (mitoxantrone) the next day, as the doctor felt that we could see some improvement (possibly decreased swelling in the leg) with the chemo treatment. We also had him on tramadol to help with the pain and discomfort. However, the swelling never really went down, as his leg was very swollen still after chemo, and he really was unable to walk around, now robbing his mobility, while now having a much much harder time defecating (i believe the sublumbar lymph nodes were swollen all along, which i believe pushed against his bowel, making it extremely hard to defecate). Not to mention the chemo made him nauseous, and didn’t have much of an appetite. His quality of life diminished very quickly, quicker than we could have ever imagined. We cherished every day, as we knew things were going downhill. About 5-6 days after the first chemo treatment, we were contemplating ending his suffering, as he was in pain, and the tramadol didn’t seem to be helping much anymore. He lost pretty much all joy in life, and that same night, as he was laying down in his bed, started bleeding from his nose uncontrollably. We had to rush him to the vet again, but this time, knowing in the back of our minds that this would be the last time we would be with him. We had to put him to sleep that night, and the doctor agreed, as the cancer had advanced so quickly and caused other complications.

    It all happened so fast. He was healthy happy dog on July 24, 2012, and died on August 29, 2012. We had done everything possible without being too invasive, but in the end, the cancer got the best of him.

    I just wanted to post this story for anyone else going through this terrible disease. There are others that have gone and are going through it as well, and my heart goes out to each and every one of you. Be strong. Don’t stop spoiling them. And have as much fun as possible in the time you have left, as you just never know when it may be the last day. Keep trying to beat the odds! We can’t let cancer keep winning.

    • Dr. Susan Ettinger on September 7, 2012 at 12:00 pm

      I am truly so sorry about your loss of Eli. It is never easy. Four years after the loss of my Paige, I still miss her terribly. Try to hold onto the good memories shared through the years to help you through the pain now.
      With sympathy, Dr Sue

  9. Bill on May 1, 2012 at 11:38 am

    Just took my dog to the vet to have a lump examine. Doctor says the lump is too small to aspirate. Is that true? If so, how big does it have to get?

    • Dr. Demian Dressler on May 9, 2012 at 4:18 pm

      Dear Bill
      I’ve successfully aspirated growths down to about 3/16″ in diameter.
      Hope this helps
      Dr D

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