How is cancer diagnosed?

Cancer is diagnosed based on an individual's symptoms, the results of a physical examination, and sometimes the results of screening tests. Confirmation that cancer is present requires diagnostic tests.

• Screening: Screening tests serve to detect the possibility that a cancer is present before symptoms occur. Screening tests are an important prophylactic measure for detecting cancer early, and healthcare professionals recommend cancer screening. Screening tests usually are not perfect; results are confirmed or disproved with further examinations and tests. Diagnostic tests are performed once a doctor suspects that an individual has cancer.
• Diagnosis: Generally, when a doctor first suspects cancer, some type of imaging study, such as X-ray, ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI), is performed. Although these tests can show the presence, location, and size of an abnormal mass, they usually can not confirm that cancer is the cause. Cancer is confirmed by finding cancer cells on microscopic examination of samples from the suspected area. Usually, the sample must be a piece of tissue, although sometimes examination of the blood is enough (such as in leukemia). Obtaining a tissue sample is termed a biopsy. Biopsies can be performed by cutting out a small piece of tissue with a scalpel (surgical knife), but very commonly, the sample is obtained using a hollow needle. Such tests are commonly done without the need for an overnight hospital stay (called outpatient procedures). Doctors often use ultrasonography or a computerized tomography (CT) scan to guide the needle to the right location. Because biopsies can be painful, the individual is usually given a local anesthetic (such as lidocaine or Xylocaine®) to numb the area.
• Staging: After cancer is diagnosed, it is staged. Staging is the process of finding out how far the cancer has spread. Staging the cancer is a vital step in determining treatment choices, and it will also give the healthcare team a clearer idea of the outlook for recovery. There can be several different processes for staging each individual cancer, such as with brain cancer, lymphoma, or melanoma.

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Cancer diagnosis is the process of determining whether a patient has cancer and, if so, what type. Most cancers are diagnosed by biopsy, the removal of some (or occasionally all) of the tissue from a mass or tumor. A biopsy may be performed by a surgeon, radiologist, or other medical specialist. Some primary care physicians even perform skin biopsies in their office. The biopsy tissue is then sent to a laboratory, where trained technologists cut the tissue into thin sections and prepare it to be reviewed by a medical specialist called a pathologist. The pathologist will view the tissue on a slide under a microscope. Special studies or stains may also be performed on the tissue to determine its type. The first decision that this physician must make is whether the tissue is malignant (cancer) or benign (not cancer). Next, if the tissue is found to be malignant, the pathologist must decide what type of cancer is present.