Diagnosis

Diagnosis encompasses screening, testing, and a physical examination. After cancer is diagnosed, it is staged. Staging is a way of noting how advanced the cancer has become, including such criteria as how big it is and whether it has spread to other organs.

Screening

Screening tests serve to detect the possibility that a cancer is present before symptoms occur. Screening tests usually are not definitive; results are confirmed or disproved with further examinations and tests. Diagnostic tests are performed once a doctor suspects that a person has cancer.

Although screening tests can help save lives, they can be costly and sometimes have psychologic or physical repercussions. Screening tests can produce false-positive results--results that suggest a cancer may be present when it actually is not. False-positive results can create undue psychologic stress and can lead to other tests that are expensive and risky. Screening tests can also produce false-negative results--results that show no hint of a cancer that is actually present. False-negative results can lull people into a false sense of security. For these reasons, health care practitioners carefully consider whether or not to perform such tests. Doctors try to determine whether a particular person is at special risk for cancer--because of age, sex, family history, previous history, and lifestyle--before they choose which screening tests to perform.

In women, two of the most widely used screening tests are the Papanicolaou (Pap) test to detect cervical cancer and mammography to detect breast cancer. Both screening tests have been successful in reducing the death rates from these cancers in certain age groups.

In men, a common screening test involves measuring the level of prostate-specific antigen (PSA) in the blood. PSA levels are high in men with prostate cancer, but levels are also elevated in men with noncancerous (benign) enlargement of the prostate. Whether the PSA test should be used routinely to screen for prostate cancer is unresolved. The main drawback to its use as a screening test is the large number of false-positive results, which generally lead to more invasive tests.

In both men and women older than 40, a common screening test involves checking the stool for blood that cannot be seen by the naked eye (occult blood). Finding occult blood in the stool is an indication that something is wrong in the colon. The problem may be cancer, although many other disorders can also cause small amounts of blood to leak into the stool. In addition, taking an aspirin or another nonsteroidal anti-inflammatory drug (NSAID) or even eating red meat can temporarily produce a positive result. Positive results can occasionally be caused by consuming poultry, fish, certain raw fruits and vegetables (turnips, cauliflower, red radishes, broccoli, cantaloupe, horseradish, and parsnips), and vitamin C.

Some screening tests can be done at home. For example, monthly breast self-examinations are valuable in helping women detect breast cancer. Periodically examining the testes can help men detect testicular cancer, one of the most curable forms of cancer, especially when diagnosed early. Periodically checking the mouth for sores can help detect mouth cancer in an early stage.

See the table Cancer Screening Recommendations.

Diagnostic Tests and Staging

Tumor markers are substances secreted into the bloodstream by certain tumors. However, tumor markers sometimes are present in the blood of people who do not have cancer. Thus, finding a tumor marker does not necessarily mean a person has cancer. However, in people who do have cancer, tumor markers can be used to monitor the effectiveness of treatment and to detect possible recurrence of the cancer. The level of a tumor marker increases if the cancer recurs.

See the table Selected Tumor Markers.

When cancer is diagnosed, staging tests help determine how advanced the cancer is in terms of its location, size, growth into nearby structures, and spread to other parts of the body. People with cancer sometimes become impatient and anxious during staging tests, wishing for a prompt start of treatment. However, staging allows doctors to determine the most appropriate treatment as well as helping to determine prognosis.

Staging may use scans, such as bone scans, or other imaging tests, such as computed tomography (CT) or magnetic resonance imaging (MRI), to determine whether the cancer has spread.

Ultrasound scanning is a painless, noninvasive procedure that uses sound waves to show the structure of internal organs. It is helpful for identifying and determining the size of certain cancers, particularly of the kidneys, liver, pelvis, and prostate. It can also be used in staging a cancer. Doctors often use ultrasound to guide the removal of tissue samples during a needle biopsy.

Computed tomography (CT) scanning is used to detect cancer in many parts of the body, including the brain and lungs and parts of the abdomen, including the adrenal glands, lymph nodes, liver, and spleen. Such detection is useful in diagnosing and staging a cancer. Magnetic resonance imaging (MRI) is an alternative to CT. With this procedure, a very powerful magnetic field generates exquisitely detailed anatomic images. MRI is of particular value in detecting cancers of the brain, bone, and spinal cord. No x-rays are involved, and MRI is extremely safe. An MRI can often be used for people who have allergic or other reactions to the radiopaque dye that is commonly injected during CT. CT and MRI scans have largely replaced the use of liver scans for evaluation of the liver and the use of lymphangiograms for the evaluation of abdominal and pelvic lymph nodes.

Positron emission tomography (PET) can also be used to help diagnose and stage cancer. A PET scan images a cancer by measuring biochemical processes within it. The test is not routinely used as a part of screening for cancer.

Biopsies are often needed to be sure that an abnormality discovered on an imaging test is cancer; biopsies are important in both diagnosis and staging. Many kinds of biopsies can be performed with a needle and do not require surgery. Sometimes, however, surgery is needed to obtain a sample of tissue. For example, a laparotomy (an abdominal operation) allows the surgeon to sample internal lymph nodes while at the same time removing a colon cancer. During the operation, the surgeon can inspect the area, including the liver, to check for spread of the cancer. During surgery for breast cancer, the surgeon performs a biopsy of lymph nodes in the armpit to determine how far breast cancer has spread and whether further treatment is needed after surgery. An operation to remove the spleen (splenectomy) for examination helps in staging Hodgkin's disease.

See the table Tests for Diagnosing and Staging Cancers.