Overview of Biopsy Principles and Surgical Oncology
Stephen Withrow United States
One of the most important steps in the management of the cancer patient is the procurement and interpretation of an accurate biopsy specimen. Not only will the biopsy provide a diagnosis but also it will help predict biologic behavior, which aids in determining the type and extent of treatment that should be afforded.
The common goal with any biopsy technique is to procure enough neoplastic tissue to establish an accurate diagnosis. Which procedure to use will often be determined by your goals for the case, site of the mass, equipment available, general status of the patient, and personal preference and experience. An accurate tissue diagnosis should be attained before treatment for the following two reasons:
If the type of treatment (surgery vs. radiation vs. chemotherapy, etc.) or the extent of treatment (conservative vs. aggressive resection) would be altered by knowing the tumor type. A biopsy is particularly important if the surgery is in a difficult location (e.g., distal extremity, tail, or head and neck) for reconstruction or if the proposed procedure carries significant morbidity (e.g., maxillectomy or amputation).
If the owners’ willingness to treat their pet would be altered by knowledge of tumor type and therefore, prognosis, a biopsy is desirable before major therapeutic intervention.
General Guidelines for Tissue Procurement and Fixation
1. The proper performance of an incisional or needle biopsy does not increase the rate of metastasis. On the other hand, cancer cells may be allowed to contaminate the tissues surrounding the mass, making resection more difficult. The biopsy site should be planned so that it may be subsequently removed along with the entire mass.
2. Avoid biopsies that contain only ulcerated or inflamed tissues.
3. Several samples from one mass are more likely to yield an accurate diagnosis than a single sample.
4. Small biopsies should not be obtained with electrocautery, as it tends to deform (by autolysis or polarization) the cellular architecture.
5. If evaluation of margins of excision is desired, it is best if the surgeon marks the specimen (fine suture or ink on questionable edges) or submits margins in a separate container.
6. Tissue is generally fixed in 10% buffered neutral formalin with one part tissue to ten parts fixative.
7. Tissue should not be thicker than 1 centimeter or it will not fix deeply. Large masses can be cut into appropriate sized pieces and representative sections submitted or sliced like a loaf of bread, leaving one edge intact, to allow fixation. After fixation (two to three days), tissue can be mailed with a 1:1 ratio of tissue to formalin.
8. A detailed history should accompany all biopsy requests!
The more commonly used methods of tissue procurement are needle punch biopsy, incisional biopsy, and excisional biopsy. All have indications depending on a number of variables such as tumor size, location, presence of ulceration, and likelihood of malignancy.
Interpretation of Results
The pathologist’s job is to determine: 1) tumor vs. no tumor, 2) benign vs. malignant, 3) histologic type, 4) grade (if available and clinically relevant), and 5) margins (if excisional). Many pitfalls can take place to render the end result inaccurate. Potential errors can take place at any level of diagnosis and it is up to the clinician in charge of the case to interpret the full meaning of the biopsy result. As high as 10% of biopsy results are inaccurate in a clinically significant sense. If the biopsy result does not correlate with the clinical scenario, several options are possible:
1. Call the pathologist and express your concern over the biopsy result. This exchange of information should be helpful for both parties and not looked upon as an affront to the pathologist’s authority or expertise. It may lead to:
a. Re-sectioning of available tissue or paraffin blocks.
b. Special stains for certain possible tumor types (e.g., toluidine blue for mast cells).
c. A second opinion by another pathologist.
2. If the tumor is still present in the patient, and particularly, if widely varied options exist for therapy, a second (or third) biopsy should be performed.
A carefully performed, submitted, and interpreted biopsy may be the most important step in management and subsequent prognosis of the patient with cancer. All too often tumors are not submitted for histologic evaluation after removal because “the owner did not want to pay for it.” Biopsies should not be an elective owner decision. Because of increasing medicolegal concerns, it is not medical curiosity alone that mandates knowledge of tumor type.
The vast majority of solid tumors in animals will be treated with surgery. Surgery can be used to prevent cancer (e.g., ovariohysterectomy in young dogs prevents later development of mammary cancer), diagnose cancer (biopsy), provide palliation (removal of necrotic oral tumor in a dog with metastasis), debulk a tumor to enhance response to radiation or chemotherapy, or surgery can be used with curative intent.
Just like radiation and chemotherapy, surgery can be administered by dose. The commonly used doses are intralesional (shelling out a lipoma), marginal (on the pseudocapsule, often leaves microscopic residual disease), wide (in excess of 1 cm margins), and radical (entire compartment, e.g., amputation). Tumor site, tumor grade, tumor stage, and species affected determine the needed surgical dose. If curative intent surgery has been performed, it is imperative to properly submit the entire specimen (fixed and inked) for assessment of grade and adequacy of removal (margins). Incomplete margins require immediate re-intervention with a second surgery, radiation, or chemotherapy rather than waiting for the inevitable local recurrence and possible metastasis. Aggressive surgical resection such as mandibulectomy, maxillectomy, orbitectomy, nasal planum resection, amputation, limb sparing, rib removal, and hemipelvectomy are generally tolerated well with acceptable cosmetic and functional outcomes. Proper attention to analgesia, anesthesia, and postoperative support are vital to a successful outcome.
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