A physical exam and medical history, especially the history of symptoms, are the first steps in diagnosing cancer. In many instances, the medical caregiver will order a number of tests, most of which will be determined by the type of cancer and where it is suspected to be located in or on the person's body. In addition, most caregivers will order a complete blood count, electrolyte levels and, in some cases, other blood studies that may give additional information (for example, a PSA or prostate specific antigen test may guide the caregiver to do additional tests, such as a prostate biopsy).
Imaging studies are commonly used to help physicians detect abnormalities in the body that may be cancer. X-rays, CT and MRI scans, and ultrasound are common tools used to examine the body. Other tests such as endoscopy, which with variations in the equipment used, can allow visualization of tissues in the intestinal tract, throat, and bronchi that may be cancerous. In areas that cannot be well visualized (inside bones or some lymph nodes, for example), radionuclide scanning is often used. The test involves ingestion or IV injection of a weakly radioactive substance that can be concentrated and detected in abnormal tissue.
The preceding tests can be very good at localizing abnormalities in the body; many clinicians consider that some of the tests provide presumptive evidence for the diagnosis of cancer. However, in most patients, the definitive diagnosis of cancer is based on the examination of a tissue sample from the tissue that may be cancerous by a qualified pathologist. Some biopsy samples are relatively simple to procure (for example, skin biopsy or intestinal tissue biopsy done with an endoscope equipped with a biopsy attachment). Other biopsies may require surgery (for example, brain tissue or lymph node biopsy). In some instances, the surgery to diagnose the cancer may result in a cure if all of the cancerous tissue is removed at the time of biopsy.
The biopsy can provide more than the definitive diagnosis of cancer; it can identify the cancer type (for example, a primary or metastatic type of brain cancer) and the "stage" of the cancerous cells. The stage or cancer staging is a way for clinicians and researchers to estimate how advanced or how severe the disease is. The following section describes the general staging methods for cancers.