Article provided by Jaime F. Modiano, VMD, PhD and reprinted with permission from the Modiano Lab web site (www.modianolab.org)

Our success in treating diseases in people and their pets is dependent in large part on our ability to correctly diagnose and stage such diseases. Here, we will review why and when a biopsy may be indicated to diagnose and stage tumors (cancer), but the same principles apply to many other diseases.

First, we should answer the question, what is a biopsy? According to the definition provided by the National Cancer Institute, a biopsy (By-op-see) is the removal of cells or tissues (from a growth, organ, or lesion) for examination by a pathologist. The pathologist may study the tissue under a microscope or perform other tests on the cells or tissue.

There are several different types of biopsies that can be performed: an incisional biopsy is when only a sample of tissue is removed; when an entire lump or suspicious area is removed, the procedure is called an excisional biopsy. Finally, when a sample of tissue or fluid is removed with a needle, the procedure is called a needle biopsy, core biopsy, or fine-needle aspirate. Any of these types of samples may provide the pathologist sufficient information to make a diagnosis of cancer. However, the rule “more is better” generally applies when it is important to accurately classify and stage that cancer.

Generally, physicians and veterinarians follow a deliberate, systematic process to diagnose an ailment. This includes a thorough history and physical exam, followed sequentially by laboratory tests that help eliminate or “rule out” possibilities that can explain the signs and symptoms. In the case of cancer, a high index of suspicion can be achieved using non-invasive tests, such as radiographs, ultrasound, or magnetic resonance imaging, but a definitive diagnosis requires examination of the affected tissues. It is at this point where the pros and cons of each type of biopsy need to be considered.

The least invasive procedure is a fine needle aspirate. For this procedure, the patient is usually awake or only lightly sedated, a needle is inserted into the abnormal tissue, and negative pressure is applied with a syringe to aspirate cells into the needle and the syringe hub. The cells that were aspirated can then be placed on a glass slide for microscopic examination (cytopathology), or they can be placed in a preservative for other tests. The advantages of the procedure are that it is minimally invasive and generally very safe, it is less costly than an incisional or an excisional biopsy, and the results can be obtained rapidly, especially because the attending physician or veterinarian can provide a preliminary assessment of the microscopic appearance of the sample. The disadvantages are that the tissue architecture is destroyed, and so the information that can be gleaned from the sample is limited. Furthermore, extensive training and experience are necessary to be able to provide a definitive cytopathology interpretation from fine needle aspirates, and even the most experienced pathologists can sometimes only provide a tentative diagnosis from aspirate samples that do not have the benefit of a “tissue context”. Finally, the amount of sample is limiting, and so additional tests require additional samples. In general, a fine needle aspirate is a suitable first-line approach to narrow the list of differential diagnoses, although in many cases, it can provide all the information needed to formulate a treatment or management plan.

Incisional biopsies are, by nature, more invasive than fine needle aspirates. However, contemporary tools allow biopsies to be obtained safely and at reasonable cost. Often, a “tru-cut” biopsy tool, which is similar to a needle with a larger gauge or channel, can be used in a manner that is only slightly more invasive than a fine needle aspirate. This larger needle is inserted into the tissue, and as it penetrates, it also “cuts”, allowing a small core to remain embedded within the needle channel. This core of tissue is then removed from the needle and can be used to make imprints for cytopathology, and it can be placed in a preservative for additional tests. Most often, the preservative is formalin, which is used to “fix” the tissue to prevent changes in its shape or form. The formalin-fixed tissues are then embedded in paraffin wax for processing and storage. The most common test done by a pathologist is examination of formalin-fixed and paraffin embedded tissue that has been subjected to several additional processing and staining steps under the microscope. The advantages of an incisional biopsy are that there is more tissue available for analysis, and the architecture, or the context of how cells relate to each other, are preserved. In addition, the preservation of the tissue in a paraffin block allows the pathologist to perform additional tests without the need to obtain additional samples. This provides a more complete picture to accurately classify and stage the disease. Because tissue imprints can be obtained from these samples, a provisional diagnosis can also be obtained. The disadvantages are that it is more invasive (it usually requires at least a small “nick” in the skin to allow the needle to be placed into the tissue), it requires heavy sedation or general anesthesia, it takes longer to process and read, and consequently, it is more costly. In some cases, it is necessary to remove a large piece of tissue (“wedge biopsy”) in order to provide the pathologist sufficient material to reach a diagnosis.

Excisional biopsies are done when there is an opportunity to remove the whole tumor without significantly added risk to the patient.

Biopsies and Investigational Studies

There are various cancers where fine needle aspirates have become the customary diagnostic procedure. A case in point is canine lymphoma. In approximately 9 of every 10 cases, the disease involves accessible lymph nodes that can be sampled with a small needle, the malignant cells readily dislodge from the node with slight negative pressure, and the diagnosis is usually straightforward. Some staging methods, which identify how far the disease has advanced, also do not require a precise histological classification. The presence of malignant cells, along with physical exam findings, blood tests, imaging, and analysis of a bone marrow sample are sufficient to stage the disease. Management options include various measures that range from palliative care to keep the patient comfortable for a few days to weeks, to more aggressive chemotherapy that may lead to extended remissions.

This tried-and-true approach has served the profession and its patients well for over 30 years, but recent work recognizes that staging canine lymphoma using additional criteria has value to determine the best management protocols. A biopsy allows the pathologist not only to appreciate the appearance, shape, and size of the cells (morphology), but also to gain insight into the disturbances of the architecture in the same tissue. The astute pathologist can infer if cells are expanding from a center or contracting toward a center, the proportion of normal remaining tissue within and around the tumor, the number of cells in the active process of division, and other important features. Based on this, we now recognize “lymphoma” as a group of more than a dozen different tumors, each originating from a different type of lymphocyte with different morphological and architectural features. These can have different behaviors and response to treatment, so their proper classification can be useful to evaluate progression and to guide the management of the disease in otherwise healthy dogs. Nevertheless, the cost and risk of a biopsy cannot always be justified. For example, in cases where circumstances preclude consideration of multiple treatment options, it may be less important to identify the specific type of lymphoma. These circumstances may include the presence of another severe, life-threatening disease, conditions that may limit the use of chemotherapy, and even financial considerations where available funds would be better spent on treatment, rather than on diagnostic tests.

Sometimes, the family of a cancer patient may be asked to consider participation in a clinical or investigational trial. Clinical trials are meant to test new drugs or compounds to treat a specific condition. Investigational trials are used to study the cause or behavior of a disease, and they may or may not involve treatment. Because trials are experimental by nature, benefits are usually attained by (and meant for) future generations of patients, although participants can sometimes receive tests and/or treatment at no or reduced costs. A biopsy is almost always required for participation in such trials. Therefore, whether a study is available or not, it is important for people to discuss the potential benefits, risks, and costs of a biopsy in the diagnosis of cancer. Attending veterinarians must consider the willingness of their pathology service lab to provide prompt, detailed information, as well as how this information will influence treatment decisions. The veterinarian and the family also should carefully consider if there are benefits of participation in available trials. Only in this way can we advance the standard of practice and the standard of care for cancer patients now and in the future.

Additional comment by Dr. Modiano: Tissue from excisional biopsies is also fixed in formalin for routine examination. Since there is more available, the pathologist can do more things with the tissue, like keep fresh frozen material. Normally, the techs will “trim” the tissue to include edges for examination to make sure the excision went to ~5 mm beyond the tumor margin or border (but this would only apply to solid tumors other than lymphoma). Biopsies for lymphoma are very dependent on how vets were trained. These days, most people who do a biopsy would choose to do small tru-cut biopsies or needle biopsies (even more people are trained to only do aspirates) because most of the lymph node is usually involved. Some people will do “wedge” biopsies where they actually remove a small piece of node with a scalpel rather than using a tru-cut needle. Less people will do a full lymph node excision, unless the node is large and firm and does not respond to treatment, which can indicate necrosis or infection that needs to come out.

From the Briard Medical Trust: Dr. Modiano says that it probably does not matter what type of biopsy it was (if it was properly fixed and prepared) for them to try to work with it. If you have any questions or are considering contributing biopsy tissue, please contact the Briard Medical Trust.