Biopsy And Diagnosis
Biopsy is critical, as it is the means by which tissue is acquired in order to make a definitive diagnosis. The histology (or the way it looks under the microscope) of the tumor gives the first clues to its behavior.
The requisite tissue can be obtained via needle aspiration or through open incisional or excisional biopsy methods. Open techniques constitute surgery and are performed in the operating room. These provide the most tissue for review by the pathologist, however are often not necessary, or even appropriate. Because many soft tissue sarcomas are readily palpable, needle biopsy is often all that is necessary. This is frequently performed by a radiologist under CT guidance. Incisional biopsy sometimes is necessary to attain an adequate sample of tissue. This involves making an incision in the skin, and obtaining some pieces of the tumor for evaluation. Except for the rarest of instances, excisional biopsy (removing the entire tumor as a biopsy) should be avoided with suspected sarcomas, as a well-planned, definitive resection after appropriate staging and tissue diagnosis is preferred (Gebhardt and Buecker, ESUN V1N5).
The Need for a Specialist
The decision to remove part of the mass or the entire mass at the time of biopsy is extremely critical. The importance of having a sarcoma specialist either perform the actual biopsy or guide the treating surgeon in planning a biopsy can not be overstated.
The biopsy is often the first step to a successful limb-sparing procedure. The location of the biopsy incision and technical aspects of obtaining tissue can have a major impact on subsequent operations (Ref. 28) (Morris, ESUN V2N2).
The Biopsy Procedure
Two types of biopsies are possible: incisional and excisional. Incisional biopsies involve only taking a small sample of the tumor and include needle (closed) and open biopsies. Needle biopsies can be either fine needle or core. Excisional biopsies are performed when the mass is small (< 2 inches) and not next to any vital structures The type of biopsy chosen must be carefully determined after evaluating the size and location of the tumor as well as the age of the patient (Mankin 1996; Simon 1998).
The placement of the biopsy site relative to the location of the tumor and the anatomic structures of the patient is also of critical importance. Small, superficial lesions are amenable to excisonal biopsy. Generally, if a malignant bone tumor is suspected, an excisional biopsy is rarely, if ever utilized. This is due to the fact that the tumor is often large at presentation and that neoadjuvant therapy is usually appropriate prior to definitive resection. If the lesion is most likely benign based upon the preoperative history, physical exam and imaging studies, then at the time of excision a frozen section should be obtained if there is any doubt as to the diagnosis. Primary excision of an expendable bone should only be considered by an experienced musculoskeletal oncologist. Expendable bones may include a rib, clavicle, sternum, ilium, scapular body and perhaps distal ulna.
Most bone tumors of uncertain biologic potential, where there is a significant suspicion for malignancy, are biopsied via an incisional approach. The location of the biopsy site is determined by a thorough prebiopsy assessment of the extent of local disease and its relationship to critical structures such as the neurovascular bundle. This must be determined on a case-by-case basis. It is strongly recommended that the biopsy be performed by the surgeon who will be performing the definitive resection so that the biopsy tract can be ellipsed within the planned surgical incision. At the time of biopsy, the surgeon must be familiar with orthopaedic oncologic principles of flap development, coverage and even amputation, when definitive limb salvage is the proposed plan for a given bone tumor.
Needle (closed) biopsies can potentially expedite the diagnostic process when performed as an outpatient in the doctor’s office. This can be conducted using a local anesthetic and can reduce the cost of the procedure. However, such techniques are generally not recommended for children. Most malignant bone tumors have a soft tissue component on its periphery. Conveniently this is also the most representative tissue. Accordingly, deep deployment of the needle within the tumor is unnecessary and likely to lead to problems such as deep contamination and bleeding. Again the needle biopsy site must be carefully planned so that it may be excised at time of resection. With a well-trained cytopathologist, fine needle biopsy is an option. A 0.7 mm diameter needle is generally used. Up to 90% diagnostic accuracy has been reported, with bone sarcomas exceeding 80% accuracy. The drawback is that insufficient material may be obtained to perform cytogentics, flow cytometry, gene profiling and other tests that may help to establish the diagnosis.
Core biopsies are minimally invasive, can be performed under local anesthesia when appropriate, maintains the architecture of the tissue and can obtain adequate specimen for advanced studies. Diagnostic accuracy for this technique can surpass 95%.
While needle biopsies are intended to faciliate diagnosis they can also lead to a delay. Because no specific diagnosis of a malignancy should be rendered on a frozen analysis, the patient must wait until the results are finalized which may take several days, if special studies are necessary. If the specimen is indeterminate, which can occur in 25-33% of cases, even at experienced centers, then a delay occured.
An open incisional biopsy can potentially be done in the office. However for suspected bone malignancies, it is usually recommended that they be performed in the operating room. Generally, longitudinal incisions are the rule. Transverse incisions potentially contaminate flap planes and can compromise neurovascular structures. During the approach to the tumor, no flaps should be developed to minimize contamination. The area where the tumor is most superficial is preferable unless other factors, such as an overlying vessel or nerve, preclude it. Furthermore, the preoperative imaging may suggest that a specific area within the tumor may be more diagnostic than another. Areas of extensive necrosis and/or hemorrhage can be misleading. Once the tumor is reached, the biopsy should involve the periphery only. Deep sampling is not necessary. A frozen section must be obtained to determine if diagnostic tissue has been retrieved but not to establish the definitive diagnosis. Careful communication with the pathologist should be done preoperatively to clarify the amount of tissue that may be necessary for special studies and any special processing of the tissue once it is explanted. Formaldehyde fixes the tissue, preventing the application of cytogentics and other molecular tests. Furthermore, the tissue rapidly desiccates once outside the body, which also prevents certain advanced tests, so expeditious handling of the specimen is very important.
For those bone tumors that have not violated the cortex, controlled fenestration will be necessary. A trephine is usually adequate but if a larger window is required it is imperative that it be round or oval to minimize stress risers. A pituitary rongeur may then be used to retrieve tissue from within the medullary canal. The bone window may then be impacted back in place and sealed with bone wax. Alternatively, a polymethylmethacrylate plug may be used instead. Hemostasis is of utmost importance. Certain tumors may be quite vascular and meticulous hemostasis may not be possible. In such cases, a drain must be placed, in line with the incision distally, and sewn in place.
The use of tourniquets is controversial. While their use provides for a bloodless approach, they must be let down prior to closure to assure adequate hemostasis. If used, the limb should not be exsanguinated to minimize the risk of tumor embolis (Randall, ESUN V1N3).
Resources about Biopsies, Immunochemistry, and Pathology Reports: The Doctor's Doctor contains several webpages that can help you in understanding a pathology report. CancerGuide contains an overview of the various types of biopsies and a pathology report. Wikipedia contains an overview of immunohistochemistry procedure. The underlying principle of immunochemical techniques is that a specific antibody will combine with its specific antigen to give an exclusive antibody-antigen structure. Wikipedia also contains an introduction to antigens and antibodies and an advanced, detailed immunochemistry reference.
Copyright © 2004 and 2005 Liddy Shriver Sarcoma Initiative.