Removing a Tumor: How Pathologists Examine Tissue

At the time of an initial biopsy, a pathologist can provide the surgeon with preliminary information, and examining its structural (histological) characteristics under a microscope. As a result of this preliminary information, the surgeon will know whether to remove the remaining tumor and how much tissue at the margins of the tumor also needs to be removed.

To obtain a more accurate diagnosis, the tissue removed during the biopsy is embedded in a block of paraffin, sliced into sections, stained, and examined under the microscope. This process usually takes a few days, and specific immunologic and molecular studies may take a week or more. All cells have a variety of proteins on their surface. Some of these proteins are called lineage specific because all cells of the same type have similar proteins. For example, certain proteins on the surface of lymph cells differ from those on the surface of cells lining the stomach. Using substances called monoclonal antibodies which are tagged with a fluorescent substance, pathologists can study a section of tissue under the microscope and, by identifying the proteins on the cells' surface, determine the type of cell involved. This procedure, called immunologic chemistry, is particularly useful when cancer cells are poorly differentiated or when the specific type of cancer must be identified, as with lymphomas.

Molecular studies. To diagnose some cancers, it may be necessary for the pathologist to identify abnormalities in the genes themselves, using molecular biology techniques. The chromosomes in a cancer cell can also be isolated and studied in the laboratory. Certain cancers have specific chromosomal abnormalities.

Lumbar Punctures
Lumbar puncture is performed in order to stage certain leukemia and lymphomas. For this procedure, after the patient receives a local anesthetic, a needle is inserted into the lumbar sac in the lower back, and a sample of spinal fluid is withdrawn. This procedure is relatively safe because the spinal cord ends above the lumbar sac (so there is little or no danger of injuring the cord). Because the spinal fluid circulates freely between the brain, the spinal cord, and the lumbar sac, lumbar punctures can also be used to inject drugs into the central nervous system to prevent disease or to administer chemotherapy to the brain.

Natural History of a Tumor
In addition to information gathered from the staging studies, when deciding on a course of treatment to recommend, the oncologist takes into account how a specific type of cancer usually behaves. This behavior, called the natural history of a tumor, is an important factor in selecting the appropriate treatment regimen for a specific cancer. Some cancers are extremely aggressive: they invade the surrounding tissue and spread quickly throughout the body. Others remain stable for many years without treatment (these "indolent" cancers include some extremely early prostate cancers, chronic leukemia, and low-grade lymphomas). In considering the natural history of the tumor in order to choose treatment, the oncologist attempts to determine, as accurately as possible, die answers to these questions:

1. How is the cancer likely to behave if it is not treated?
2. How long will it be before the patient develops symptoms?
3. Is the cancer likely to spread and, if so, to what organs?
4. Will the disease be cured by a local treatment?
5. Will the patient require more surgery?
6. Will the cancer cells be killed by radiation therapy or chemotherapy, or will they be resistant to these treatments?
7. Will a combination of treatments be best?
8. Should an experimental treatment be recommended?

Despite what we know about the natural history of a specific kind of cancer, it is not possible to answer many of these questions precisely for a specific individual, and what we know about the natural history of a cancer may not hold true for a specific individual. Nevertheless, the natural history of the cancer forms a very important part of the "big picture" when oncologists select treatments.

Source: Treatment of Acute Leukemias by Ching-Hon Pu