Cancer is suspected based on a person's symptoms, the results of a physical examination, and sometimes the results of screening tests. Occasionally, x-rays obtained for other reasons, such as an injury, show abnormalities that might be cancer. Confirmation that cancer is present requires other tests (termed diagnostic tests). After cancer is diagnosed, it is staged. Staging is a way of describing how advanced the cancer has become, including such criteria as how big it is and whether it has spread to neighboring tissues or more distantly to lymph nodes or other organs.
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 done 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 is 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, there are only a small number of screening tests that are considered reliable enough for doctors to use routinely.
Doctors determine whether a particular person is at special risk for cancer—because of age, sex, family history, previous history, or lifestyle—before they choose to perform screening tests. The American Cancer Society has provided cancer screening guidelines that are widely used. Other groups have also developed screening guidelines. Sometimes recommendations vary among different groups, depending on how the groups' experts weigh the relative strength and importance of available scientific evidence.
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, prostate-specific antigen (PSA) levels in the blood may be used to screen for prostate cancer. PSA levels are high in men with prostate cancer, but levels also are elevated in men with noncancerous (benign) enlargement of the prostate. As such, 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. Whether the PSA test should be used routinely to screen for prostate cancer is unresolved, with varying recommendations from different groups. Men over 50 should discuss the PSA test with their doctor.
A common screening test for colon cancer 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 somewhere in the gastrointestinal tract. The problem may be cancer, although many other disorders, such as ulcers, hemorrhoids, diverticulosis (small pouches in the colon wall), and abnormal blood vessels in the intestinal walls, 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 on the most commonly used test can occasionally be caused by consuming certain raw fruits and vegetables (turnips, cauliflower, broccoli, melons, radishes, and parsnips). Some people with blood in the stool may have negative test results because they have consumed vitamin C. Newer screening tests for occult blood that use a different technique are much less susceptible to such errors but are somewhat more costly. Outpatient procedures such as sigmoidoscopy and colonoscopy are also often used for colon cancer screening.
Some screening tests can be done at home. For example, monthly breast self-examinations may help women detect breast cancer. Periodically examining the testes may help men detect testicular cancer, one of the most curable forms of cancer, especially when diagnosed early. Checking the mouth for sores may help detect mouth cancer in an early stage.
Tumor markers are substances secreted into the bloodstream by certain tumors. It was first thought that measuring levels of these markers would be an excellent way to screen asymptomatic people for cancer. However, tumor markers are often present to some extent in the blood of people who do not have cancer. Finding a tumor marker does not necessarily mean a person has cancer, and tumor markers have a very limited role in cancer screening.
Diagnostic Tests and Staging
Usually, when a doctor first suspects cancer, some type of imaging study, such as x-ray (see Common Imaging Tests: Plain X-Rays), ultrasonography (see Common Imaging Tests: Ultrasonography), or computed tomography (CT—see Common Imaging Tests: Computed Tomography), is done. For example, a person with chronic cough and weight loss might have a chest x-ray or a person with recurrent headaches and trouble seeing might have CT or magnetic resonance imaging (MRI—see Common Imaging Tests: Magnetic Resonance Imaging) of the head. Although these tests can show the presence, location, and size of an abnormal mass, they cannot 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 adequate (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, but very commonly the sample is obtained using a hollow needle. Such tests are commonly done without the need for an overnight hospital stay (outpatient procedure). Doctors often use ultrasonography or CT to guide the needle to the right location. Because biopsies can be painful, the person is usually given a local anesthetic to numb the area.
In people with findings on examination or imaging tests that suggest cancer, measuring blood levels of tumor markers may provide additional evidence for or against the diagnosis of cancer. In people who have been diagnosed with certain types of cancer, tumor markers may be useful to monitor the effectiveness of treatment and to detect possible recurrence of the cancer. For some cancers, the level of a tumor marker drops following treatment and increases if the cancer recurs.
When cancer is diagnosed, staging tests help determine how extensive 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 help to determine prognosis.
Staging may use scans or other imaging tests, such as x-ray, CT, MRI, bone scintigraphy, or positron emission tomography (PET). The choice of staging test(s) depends on the type of cancer. CT 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. MRI is of particular value in detecting cancers of the brain, bone, and spinal cord.
Biopsies are often needed for staging and can sometimes be done together with the initial surgical treatment of a cancer. For example, during a laparotomy (an abdominal operation) to remove colon cancer, a surgeon removes nearby lymph nodes to check for spread of the cancer. During surgery for breast cancer, the surgeon biopsies or removes lymph nodes located in the armpit to determine whether the breast cancer has spread there. This information, along with features of the primary tumor, helps the doctor determine whether further treatment is needed. When staging is based only on initial biopsy results, physical examination, and imaging, the stage is referred to as clinical. When the doctor uses results of a surgical procedure or additional biopsies, the stage is referred to as pathologic. The clinical and pathologic stage may differ.
In addition to imaging tests, doctors often obtain blood tests to see if the cancer has begun to affect the liver, bone, or kidneys.
Last full review/revision October 2006 by Matthew G. Fury, MD