A biopsy is a procedure that removes a sample of tissue from a tumor to see if it is a type of cancer. The piece of tissue is looked at under a microscope and other tests might be done on the sample as well. A physical exam or imaging test might suggest that a tumor is a sarcoma, but a biopsy is the only way to be certain that it is a sarcoma and not another type of cancer or a benign disease.
Several types of biopsies are used to diagnose sarcomas. Doctors with experience in these tumors will choose one, based on the size and location of the tumor. Most experts prefer a fine needle aspiration or a core needle biopsy as the first step.
Fine needle aspiration (FNA) biopsy
In FNA, the doctor uses a thin needle and a syringe to withdraw small pieces of tissue from the tumor mass. When the mass is near the surface of the body, the doctor can often aim the needle while feeling the tumor. If the mass is too deep to feel, the doctor can guide the needle while viewing a computed tomography (CT) scan. The main advantage of FNA is that it can be used to biopsy tumors deep in the body without surgery. The disadvantage is that the thin needle may not remove enough tissue to make a precise diagnosis.
FNA is often useful in showing that a mass first thought to be a sarcoma (found on physical exam or imaging tests) is really another type of cancer, a benign tumor, an infection, or some other disease. But if FNA results suggest a sarcoma, another type of biopsy will usually be done to remove enough tissue to confirm that diagnosis. After a sarcoma is diagnosed, FNA is most useful in determining whether additional tumors in other organs are metastases.
Core needle biopsy
Core needle biopsies use a needle that is larger than the FNA needle. Sometimes this needle is called a Tru-Cut needle. It removes a cylindrical piece of tissue about 1/16 inch across and 1/2 inch long. It usually removes enough tissue to see if a sarcoma is present. Like FNA, CT scans can be used to guide the needle into tumors of internal organs.
In a surgical biopsy, the entire tumor or a piece of the tumor is removed during an operation. There are 2 types of surgical biopsies, excisional and incisional. In an excisional biopsy, the surgeon removes the entire tumor. In an incisional biopsy, only a piece of a large tumor is removed. An incisional biopsy almost always removes enough tissue to diagnose the exact type and grade of sarcoma. If the tumor is near the skin surface, this is a simple operation that can be done with local or regional anesthesia (numbing medication given near the mass or into a nerve). But if the tumor is deep inside the body, general anesthesia is used (the patient is asleep).
If a tumor is rather small, near the surface of the body, and not located near critical tissues (such as important nerves or large blood vessels), the doctor may choose to remove the entire mass and a margin of normal tissue in an excisional biopsy. This surgery combines the biopsy and the treatment into one operation, so it should only be done by a surgeon who has experience with treating sarcomas.
If the tumor is large, then an incisional biopsy is needed. Only a surgeon experienced in sarcoma treatment should perform this procedure.
You might want to ask about your surgeon’s experience with this procedure. Proper biopsy technique is an important part of successfully treating soft tissue sarcomas. An improper biopsy can lead to tumor spread and problems removing the tumor later on. An incisional biopsy in the wrong place or an excision without wide enough margins can make it harder to completely remove a sarcoma later on. To prevent these problems, these 2 types of biopsies should only be done by a surgeon experienced in treating sarcomas. It is best that an incisional biopsy be done by the same surgeon who will later remove the entire tumor (if a sarcoma is found).
Testing biopsy samples
The tissue removed will be looked at under the microscope to see if cancer is present. If cancer is present, the doctor will try to determine what kind it is (sarcoma or carcinoma.)
Grading: If a sarcoma is present, the biopsy will be used to determine what type it is and its grade. The grade of a sarcoma is based on how the cancer cells look under the microscope. In grading a cancer, the pathologist (a doctor who specializes in diagnosing diseases by looking at the tissue under a microscope) considers how closely the tumor resembles normal tissue (differentiation), how many of the cells appear to be dividing, and how much of the tumor is made up of dying tissue.
Each factor is given a score, and the scores are added to determine the grade of the tumor. Sarcomas that have cells that look more normal and have fewer cells dividing are generally placed in a low-grade category. Low-grade tumors tend to be slow growing, slower to spread, and often have a better outlook (prognosis) than higher-grade tumors. Certain types of sarcoma are automatically given higher scores for differentiation. This affects the overall score so much that they are never considered low grade. Examples of these include synovial sarcomas and embryonal sarcomas.
The grade is partly used to determine the stage of a sarcoma. The official staging system divides sarcomas into 3 grades (1 to 3). The grade of a sarcoma helps predict how rapidly it will grow and spread. It is useful in predicting a patient’s outlook and helps determine treatment options.
Immunohistochemistry: Sometimes these special tests are needed to accurately determine whether a sarcoma is present and, if so, what type. Part of the biopsy sample is treated with special man-made antibodies that recognize cell proteins typical of certain kinds of sarcomas. The cells are treated with chemicals that make the cells containing the specific proteins change color. The color change is then seen under a microscope.
Cytogenetics: For this test, cells’ chromosomes are examined with a microscope to look for changes. For example, in certain types of sarcomas part of one chromosome may be abnormally attached to part of a different chromosome (called a translocation). To see the chromosomes clearly, the cancer cells usually must be grown in laboratory flasks for at least a week.
Fluorescent in situ hybridization (FISH) can sometimes be used to detect translocations and other chromosome changes without first growing the cells in the lab. Tests of chromosome changes are not required to diagnose most sarcomas, but they are sometimes very useful. And as new changes are discovered, these tests may become more important and more common.
Reverse transcription polymerase chain reaction (RT-PCR): This test is another way to find translocations in some sarcomas (such as the Ewing family of tumors, alveolar rhabdomyosarcoma, and synovial sarcoma) to confirm the type of tumor. Instead of using a microscope to look for the chromosome changes as in cytogenetic testing or FISH, RT-PCR uses chemical analysis of the RNA (a substance that is made from DNA) from genes affected by the translocation. RT-PCR testing is often able to find translocations that aren’t detected by cytogenetics.