How We Diagnose Cancer
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If you experience symptoms that you believe are the result of cancer, or if a screening test (such as a mammogram) suggests cancer, your doctor will want to diagnose the cause or reason for your symptoms or test results. To do this, your doctor may ask you about your personal and family medical history, ask you to have a physical exam, and they may order lab tests, x-rays, or other procedures to diagnose or rule-out cancer. Below are three main methods used by your doctor to diagnose or rule-out a diagnosis of cancer.
Tests of the blood, urine, or other fluids from the body can help doctors make a diagnosis. These tests can show how well an organ (such as the kidney) is doing its job. High amounts of some substances may be a sign of cancer. These substances are often called "tumor markers." However, abnormal lab results are not a sure sign of cancer. Doctors cannot rely on lab tests alone to diagnose cancer.
The National Cancer Institute (NCI) offers several fact sheets about lab tests. Go to the NCI Website and click on the "Publications" section to get fact sheets.
Imaging procedures create pictures of areas inside your body that help the doctor see whether a tumor is present. These pictures can be made in several ways:
- X-rays: X-rays are the most common way to view organs and bones inside the body.
- CT Scan: An x-ray machine linked to a computer takes a series of detailed pictures of your organs. You may receive a contrast material (such as dye) to make these pictures easier to read.
- Radionuclide Scan: A small amount of radioactive material is injected through your bloodstream and collects in certain bones or organs. A machine called a scanner detects and measures the radioactivity. The scanner creates pictures of bones or organs on a computer screen or on film. Your body gets rid of the radioactive substance quickly.
- Ultrasound: An ultrasound device sends out sound waves that people cannot hear. The waves bounce off tissues inside your body like an echo. A computer uses these echoes to create a picture called a sonogram.
- MRI: A strong magnet linked to a computer is used to make detailed pictures of areas in your body. Your doctor can view these pictures on a monitor and can print them on film.
- PET Scan: A small amount of radioactive material is injected into your bloodstream. A machine makes pictures that show chemical activities in the body. Cancer cells sometimes show up as areas of high activity.
- Endoscopy: A thin, lighted tube is used to examine organs inside the body.
In most cases, doctors need to do a biopsy to make a diagnosis of cancer. For a biopsy, the doctor removes a sample of tissue and sends it to a lab where a pathologist looks at the tissue under a microscope. The tissue sample may be collected in several ways:
- With a needle: The doctor uses a needle to withdraw tissue or fluid.
- With an endoscope: The doctor uses a thin, lighted tube (an endoscope) to look at areas inside the body. The doctor can remove tissue or cells through the tube.
- With surgery: Surgery may be excisional or incisional.
- In an excisional biopsy, the surgeon removes the entire tumor. Often some of the normal tissue around the tumor also is removed.
- In an incisional biopsy, the surgeon removes just part of the tumor.
It is usually a combination of these main methods of testing that your physician will use to either diagnose or rule-out a diagnosis of cancer.