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Answers from vets about your dog:

What is a Biopsy and When Might Your Dog Need it?

Posted June 10, 2015 in Dog Surgery A-Z

AJ Debiasse, a technician in Stroudsburg, PA, contributed to this article.

When your dog has a mass (something unexpected in or on his body), one of the decisions you will need to make with your veterinarian is whether you should remove and test it, or test a piece of it first, and then remove it. Regardless of which option you choose, testing a piece of a mass is called a “biopsy.”

Dog at the vetHow is a biopsy performed?
A biopsy is performed by removing a small portion of the mass and sending it to a pathologist. A veterinary pathologist is a veterinary specialist who reads microscopic preparations (cells or tissue on a slide). A few specialty practices, and all veterinary schools, have a pathologist on staff. Most other practices will send the samples to an outside lab. Depending on the sample and the lab, you will typically receive results an average of 7-10 days after the procedure. A biopsy is performed under sedation or general anesthesia in most cases. Small samples can sometimes be collected after local anesthesia is used, e.g., a skin biopsy.

Click here to learn about anesthesia safety and myths.

Why might your veterinarian suggest that a mass be removed after a biopsy?
Depending on the location of the mass, it may be challenging to safely remove (excise) it in its entirety.

If a microscopic examination reveals that the mass is cancerous (malignant), your veterinarian will want to remove as much of it as possible — even if it means removing healthy tissues beyond the mass (in every direction). This can be difficult, if not impossible, in some areas where there is little extra skin (such as the foot or the leg) but it will be very important to keep the cancer from spreading.

However, if the biopsy reveals that the mass is benign, then less healthy tissue needs to be removed. In this situation, the biopsy will change the invasiveness of the surgery.

Why might your veterinarian suggest that a mass be removed before a biopsy?
When a mass is small, it may not be much more invasive to remove it completely than to take a biopsy first. The smaller the mass, the easier it is to remove, meaning a less invasive surgery for your dog and a smaller bill for you.

Delaying treatment by performing a biopsy first is not always ideal either. Even if a mass is benign, if it's causing a blockage or mobility issues, it should be removed right away. In these cases, since a biopsy would not change the immediate treatment plan, it is reasonable, if not advisable, to go straight to surgery.

For very aggressive masses, actively bleeding masses or rapidly declining patients, delaying treatment is again not recommended. Waiting 7-10 days for biopsy results could make the difference between life and death, or could cause additional suffering. Performing a biopsy and then removing it also means that your dog will be undergoing anesthesia twice in a short period of time. If your dog is healthy, the risk is minimal. But if your dog is sick, your veterinarian may decide it’s safer to opt for removal without a preliminary biopsy to minimize the potential of anesthetic complications.

Performing a biopsy first and surgery later is also more costly. Click here to learn about pet insurance so that you are never put in a position where finances keep your pet from the best possible care.

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Dr. Phil Zeltzman is a board-certified veterinary surgeon and author. His traveling practice takes him all over Eastern Pennsylvania and Western New Jersey. You can visit his website at, and follow him at