Cat and Dog Biopsy: What Are They, and Why Would a Vet Perform One?

A cat or dog biopsy is a common test that helps figure out the physical makeup of a lump or lesion. It can tell whether the area is cancerous or not.

A biopsy is a relatively quick and effective method that your veterinarian can use to diagnose your pet, which can give your furry companion the best chance for proper treatment and quicker recovery.

What Is a Cat and Dog Biopsy?

A biopsy is a surgical procedure where a part of a tissue or organ is surgically removed and sent to a veterinary pathologist for evaluation and diagnosis (called histopathology).

A biopsy can be done on:

• Suspicious lesions on or under the skin

• Lumps or bumps

• Chronic lesions or those that don’t respond to treatment

• Any organ

Biopsies of the skin are more common, but other biopsies include those of the following:

• Lymph node

• Intestinal

• Muscle

• Liver

• Spleen

• Lung

• Kidney

Biopsies can be painful, which is why they are either done with sedation or under general anesthesia. The area around the biopsy site is also numbed with a local anesthetic, typically lidocaine.

Some biopsies are taken using an ultrasound, endoscope, or during an exploratory surgery where the abdomen is opened and samples of multiple organs are taken.

Fortunately, most biopsies are done on an outpatient basis with minimal home care; most need only a few stitches and a short course of pain medication.

Types of Cat and Dog Biopsies

Some types of biopsies in dogs and cats include:

1. Excisional: Often used to remove most or all of the lesion or lump

2. Incisional: Often used to remove a part of the lesion or lump. There are varied techniques:

   • Wedge: Skin and underlying tissue or organ is cut in a V shape

   • Punch: A device is used to remove a thicker part of tissue in a circular shape

   • Shave: A thin layer of skin is removed, typically on the ear and other sensitive areas

How Does a Cat and Dog Biopsy Work?

A biopsy is a surgical procedure that removes a small piece of tissue to help give a diagnosis.

Usually, several sites (about three or four) are chosen for biopsy.

Once sent to the pathologist, the sample will be split into many tiny pieces, placed on microscope slides, stained with dyes, and then checked under the microscope.

While biopsy with histopathology is a useful diagnostic tool, at times the results can be inconclusive or unexpected.

Possible causes for this include:

• Poor timing of the biopsy—Some lesions can come and go and not be there at the biopsy appointment

• Poor lesion choice—Area of hemorrhage (bleeding) or necrosis (death of tissue)

• Poor technique—Non-diagnostic or characteristic sample, or the sample is not large enough or deep enough for diagnosis

• Errors—They can happen during shipment or processing of the sample

In these cases, more biopsies may be needed or a larger/deeper biopsy sample must be taken to reach a diagnosis.

Why Would a Cat or Dog Need a Biopsy?

The vet can’t be sure by the look of a skin mass or lump what it is or if it is cancerous. If your dog or cat has a suspicious mass or lump, they will need a biopsy.

Signs that should cause alarm and need for biopsy include:

• Sudden appearance of a lump or bump

• Loss of pigment

• Skin lesions that don’t go away or get worse despite treatment

• Unusual or severe skin lesions

• Unexplained hair loss

• Change in size/appearance of an existing lump or bump

• Discomfort or pain of a lump or bump

• Unexplained symptoms

Biopsy samples can also be sent to a laboratory for bacterial and fungal culture and sensitivity testing if a severe or resistant infection is suspected.

Why Are Cat and Dog Biopsies Important?

Biopsies help find the underlying cause of your pet’s lump or lesion: tumor (malignant or benign), autoimmune disease, severe infection, or inflammatory disease such as IBD or hepatitis.

Knowing the condition your pet has can help you find the proper steps toward getting her the care she needs and minimizing future pain and suffering.

Biopsies are important for guiding future prognostic and treatment options. They can provide a grading scheme for cancerous masses, which helps decide the surgery needed and if there will be chemotherapy or radiation.

Biopsies may be the first step toward planning the type of surgery needed to remove the mass.