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
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
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 it 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 has a fluid-filled mass, you could reasonably make an argument to your vet that you want to avoid a fine needle aspirate or a needle biopsy. That said, most veterinarians would be able to do one successfully. While I think it’s reasonable to be concerned, I would tell your vet your concern and then trust their judgment about whether they should go ahead with the procedure in your dog’s specific case. Just mentioning your worry will ensure they take even more care than they usually do.
For solid tumors within the body, there is a very low risk of spread along the needle tract. 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.
There is a 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. 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
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, arguing to avoid these, in general, has merit.
Especially because 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. Of course, this could change over time, and there are a couple of tumors in other species where biopsy does very slightly increase the odds of spread.
But in general, fine needle aspirates, needle biopsies, and biopsies, in general, 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. Demian Dressler is internationally recognized as “the dog cancer vet” because of his innovations in the field of dog cancer management, and the popularity of his blog here at Dog Cancer Blog. The owner of South Shore Veterinary Care, a full-service veterinary hospital in Maui, Hawaii, Dr. Dressler studied Animal Physiology and received a Bachelor of Science degree from the University of California at Davis before earning his Doctorate in Veterinary Medicine from Cornell University. After practicing at Killewald Animal Hospital in Amherst, New York, he returned to his home state, Hawaii, to practice at the East Honolulu Pet Hospital before heading home to Maui to open his own hospital. Dr. Dressler consults both dog lovers and veterinary professionals, and is sought after as a speaker on topics ranging from the links between lifestyle choices and disease, nutrition and cancer, and animal ethics. His television appearances include “Ask the Vet” segments on local news programs. He is the author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity. He is a member of the American Veterinary Medical Association, the Hawaii Veterinary Medical Association, the American Association of Avian Veterinarians, the National Animal Supplement Council and CORE (Comparative Orthopedic Research Evaluation). He is also an advisory board member for Pacific Primate Sanctuary.