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Diagnostic Tests: Biopsy

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Treatment Type: Diagnostic Procedures
Caregiver: Vets Only

A biopsy is a medical test involving a microscopic examination of affected cells or tissues that have been surgically removed for the purpose. A small sample of the skin with lesions of red patches that are found on the patient's skin, nails, and other body parts is taken for diagnosis. The sample is studied under a microscope for an abnormal growth of cells.

A biopsy is the only way to be sure if a tumor is benign or malignant. All treatment decisions going forward are based on this. Even if you don't want to pursue aggressive cancer therapy it is good to know what to expect.

Biopsy is best done by removing a small piece of tissue around 8-10 mm before doing anything else with the tumor. (unless the tumor is this small then just remove it all.) It is much more effect to manage a tumor if we know what it is before trying to remove all of it. Tissue biopsies show not just the cells but the their structure within the tissue. This is important for the prognosis. It's important to have a detailed conversation with your veterinarian about your goals and limitations before started any procedures.

There are a few different forms of biopsy, using different techniques:

  • During exploratory surgery, part of intestine will be sampled.
  • Endoscopy
  • Skin biopsy using fine needle aspiration
  • Bone and bone marrow biopsy

Here is a list of some of the most common dog cancers and conditions where biopsies are used as a diagnostic tool.

Bladder Cancer (Transitional Cell Carcinoma)

There are two ways that biopsy is used in bladder cancer. If a mass is detected it is used to define what type of mass it is. In some cases cancer cells are found in the urine and this is not necessary. If a mass can be surgically removed biopsy is used to tell if there are "clean margins". This means evaluating if there are cancer cells at the edge of the tissue removed. If not then the success with surgery is greater. Transitional cell carcinoma spreads in tiny lines through the wall of the bladder so it is generally not 100% removed by surgery, but if the margins look clean then there is very little cancer left and it can often be managed for years with low dose chemotherapy.

Bone Cancer (Fibrosarcoma)

Bone cancer can be suspected based on clinical signs and x-rays. X-rays normally show mottling and destruction of the bone. However, due to the fact that we can't distinguish if it's osteosarcoma, fibrosarcoma or chondrosarcoma without biopsy, and that treatment protocols are different for each of these, biopsy is mandatory before taking any action regarding treatment. A bone biopsy is usually completed under a general anaesthetic. The skin over the area of bone to be sample is clipped and aseptically prepared (throughly cleaned). A bone biopsy needle or trucut biopsy instrument is used to sample the bone. The sample is sent to the laboratory for histopathological analysis.

Bone Cancer (Osteosarcoma)

X-rays of bones affected with osteosarcoma are usually highly indicative, since there are very few things that can destroy and remodel the bone in such a manner. When you add history, age, breed on top of that, a vet can make pretty strong case without biopsy. However, due to the fact that treatment for osteosarcoma is limb amputation in most cases, or complicated bone surgery, and chemotherapy or radiation afterwards, one has to be 100% sure about diagnosis. For this reason biopsy is mandatory to confirm diagnosis, it's mostly done in two ways, first a fine needle aspirate, which can be inconclusive, because we just aspirate the tissue and it's more of a screening method. If fine needle aspiration doesn't produce conclusive diagnosis, surgical biopsy is necessary. Surgical biopsy will provide reliable diagnosis, since we can take big part of the bone so histological exam is through and conclusive.

Breast Cancer (Adenocarcinomas)

A biopsy is the best way to confirm a diagnosis of mammary cancer, and is recommended for most dogs with masses in their mammary glands. A biopsy involves removal of a small section of tissue. Biopsies are about the size of paper hole punch or a small wedge, requiring 1-2 sutures. It requires a brief period of anesthesia. The biopsy is sent to the lab, where a pathologist evaluates the tissue under a microscope. This usually takes 3-5 days. The pathologist tells us exactly what type of tumor we are dealing with. We can find out if it is malignant or benign and exactly what type of cancer it is.

With this information, we can develop appropriate therapy recommendations. Usually surgery is required to completely remove the tumor. By doing a biopsy beforehand, we will know how aggressively the tumor needs to be removed. We can also plan for appropriate chemo or radiation therapies based on the tumor type.

Sometimes we remove entire mammary tumors prior to doing a biopsy. While this is okay, it is not ideal as we may not remove enough tissue because we didn't know the exact type of tumor we were treating. On the other hand, we may aggressively remove a more benign tumor. The information we gather about a tumor from the biopsy is invaluable in planning treatment.

Joint Cancer (Synovial Sarcoma)

Biopsy is the only reliable way to diagnoses synovial sarcoma, and mandatory in these cases, since limb amputation is the best treatment modality, and you really don't want to amputate your pets limb if it's not necessary. Biopsy can be done using special Jamshidi needle, or by opening a joint and cutting out a sample. Both of these are quite invasive, but unfortunately there is no alternative for acquiring definitive diagnosis.

Liver Cancer (Hepatocellular Carcinoma)

Clinical signs, physical exam and laboratory findings are not specific in cases of HCC, they are indicative of liver disease, but not much else. Imagining diagnostics are more specific, especially advanced ones, like MRI and CT which can reliably differentiate between malignant and non-malignant hepatic masses. Despite very high specificity and sensitivity of advanced imagining techniques in differentiation of malignant disease, they can't reliably differentiate between different kinds of tumors thus a biopsy is still necessary to get a definitive diagnosis and plan an appropriate treatment protocol.

Liver Fibrosis (Juvenile Fibrosing Liver Disease)

Abdominal ultrasonography will help in determining the structure and size of liver, but a liver biopsy may be required for detailed analysis of the liver tissue.

Liver Tumor (Hepatic Nodular Hyperplasia)

Nodular hyperplasia is a benign condition which is usually diagnosed incidentally during laparotomy/laparoscopy or ultrasound examination performed because of another health problem or a routine checkup. Despite this fact it shouldn't be glanced over and declared nodular hyperplasia based on macroscopic appearance and absence of symptoms. Biopsy should always be performed on any liver lesion, because macroscopic appearance can't tell us if it's benign hyperplasia or aggressive carcinoma.

Liver Tumor (Hepatocellular Adenoma)

Hepatocellular adenomas don't cause clinical signs, unless they rupture and hemorrhage, they are usually accidental findings on x-rays or ultrasound exam, and once we find a mass on the liver, we have to do further diagnostics in order to know if we need to remove it, use chemotherapy, some other treatment or we can leave it there and keep an eye on it. Advanced imaging techniques like MRI which can reliably differentiate between malignant and non-malignant hepatic masses. Despite very high specificity and sensitivity of advanced imagining techniques in differentiation of malignant disease, they can't reliably differentiate between different kinds of tumors thus a biopsy is still necessary to get a definitive diagnosis and plan an appropriate treatment protocol.

There are two options when taking a liver biopsy, first is ultrasound guided fine needle aspiration, which easier to do, doesn't require general anesthesia nor any special preparation. Whilst this method is more convenient, it can only produce samples for cytology examination, not histology. Cytology can quite conclusive in some cases, especially for diagnosing diffuse tumors, but in general it's sensitivity is about 30-50%.

Mast Cell Tumor (Mastocytoma)

Fine needle aspirate biopsy is the commonest method used for cutaneous and subcutaneous tumors like mast cell tumors. It is an easy technique. In surgical candidates, it is recommended to remove the complete mass with wide margins of normal tissue (3 cm) as soon as possible and assess the histologic grade. Early removal of grade 1 mastocytomas are regarded as curative. Dogs with grade 2 or 3 mastocytomas or inoperable masses should be treated with radio or chemotherapy.

Prostate Cancer (Adenocarcinoma)

Collecting tissue is the only definitive way to diagnose and plan treatment for prostatic cancer. Often times this will be done through an ultrasound guided biopsy. Aspirates (collecting cells with a needle) can sometimes be revealing but are not always definitive. Knowing with certainty what is happening in the tissue is the only way to treat it for the best outcome.

Soft Tissue Sarcomas

Taking a tissue sample so that we can evaluate not only the tumor type but it's invasiveness into tissue is of huge importance. This guides us on the aggressiveness of the tumor, how far it has invaded the surrounding tissues and helps to plan the best course of treatment. Getting the sample depends on the tumor, the behavior of the dog and the location on the body. Sometimes we can use a local, sedation and sometimes we need general anesthesia.

Testicular Tumor (Seminoma)

Biopsy is the only way to be sure what a mass or a tumor actually is, however in cases of testicular tumors, full incisional biopsy is rarely performed, due to the fact that it's more complicated than removal of the tumor (neutering) and the fact that fine needle aspiration and cytology is usually enough to confirm that the enlargement of the testicle is indeed a tumor and not something else. Fine needle aspiration and ultrasound of the testicles are usually conclusive enough to get working diagnosis of testicular tumor and proceed to neutering as a treatment for this condition. Once the testicles are removed they should be sent to pathohistology exam in order to determine type of tumor.

Tongue Cancer (Squamous Cell Carcinoma)

There are multiple types of mouth cancer and they have different degrees of danger to your pet and different treatments. A biopsy sample is the only way to make clear, specific recommendations for you dog. Biopsy can involve taking just a piece of large tumors so a treatment plan can be formed without too much expense. Small tumors are generally taken off whole and if they are benign then treatment is done also.

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