Diagnosis is the process of confirming the presence of cancer and obtaining the necessary information about the cancer to make treatment decisions. If you have signs and symptoms consistent with cancer or have had a positive screening test, your doctor will order diagnostic tests, which may fall into 1 or more of the following categories:
Blood testing is the most common laboratory test. Results can be positive, negative, or fall in or out of a numerical range considered to be normal. If blood work has been done before, new numbers can be compared against previous results.
Some blood test results may lead to other diagnostic tests. Except in rare cases, such as leukemia, there is no blood test that can definitively diagnose or rule out cancer.
Blood tests can be used to:
- Identify the effects of cancer or its treatment—Drops in blood cell counts may indicate problems with cell production in the bone marrow. This can be seen with chemotherapy, radiation therapy, or cancers that have metastasized to the bone marrow.
- Detect abnormalities in specific organs, such as the liver, kidneys, or bones.
- Look for tumor markers—These are substances that are generally higher than normal in the blood, urine, or body tissues in certain types of cancer. Tumor markers are produced either by the tumor itself, by the body in response to the presence of cancer, or by certain benign (noncancerous) conditions. See the Focus box below for more information regarding tumor markers.
Currently, the main use of tumor markers is to assess a cancer's response to treatment and to check for recurrence. Scientists continue to study the uses of tumor markers including their role in the early detection and diagnosis of cancer. Most tumor markers however, cannot be routinely used for screening and diagnosis. For example, the use of prostate-specific antigen (PSA) for the early detection of prostate cancer is widely used, but remains controversial. If you are being evaluated for cancer, you may wish to ask your doctor about the role of tumor markers in the diagnosis and treatment of your specific tumor.
Table 2 briefly lists selected tumor markers, and the cancers with which they are associated.
Cirrhosis, hepatitis, ataxia telangiectasia, Wiscott-Aldrich syndrome, pregnancy
Carcinoembryonic antigen (CEA)
Inflammatory bowel disease, pancreatitis, and liver disease; Tobacco use can also contribute to higher-than-normal levels of CEA
Human chorionic gonadotropin (HCG)
Choriocarcinoma (a rare cancer of the uterus), trophoblastic disease (a rare cancer that develops from an abnormally fertilized egg), cancers of the testis, ovary, liver, stomach, pancreas, and lung
Pregnancy and marijuana use can also cause elevated HCG levels
Medullary carcinoma of the thyroid, lung cancers
Prostate-specific antigen (PSA)
Ovarian cancer, cancers of the uterus, cervix, pancreas, liver, colon, breast, lung, and digestive tract
Multiple myeloma, lymphomas
Bladder tumor antigen (BTA)
Cancer is difficult to find, especially in its early stages. However, the sooner cancer is caught, the better the outcome. Imaging techniques—methods of producing pictures of the body’s interior structures—are often extremely useful for finding early cancers far too small to detect by other means. Imaging can also be used to determine if and where the cancer has spread, to plan surgical and other forms of therapy, and to detect recurrences following treatment. While imaging tests can be highly suggestive of cancer, by themselves they are incapable of distinguishing benign from malignant tumors. A biopsy is required for this.
Imaging tests use different types of energy waves to produce pictures. These pictures can be taken all over the body. Some tests use contrast dyes to improve visibility of internal structures.
Imaging tests include:
To create an image of the chest or bones, x-rays are directed through the body and onto film. High-density tissue, such as bone, absorbs a lot of x-rays and appears white on the developed x-ray. Cancer involving bone will appear even whiter than the surrounding normal bone tissue. Low-density tissue, such as the air in your lungs absorbs few or no x-rays and appears black. Tumors in the chest typically appear gray to white on the film.
Mammograms are x-ray images of the breast. They can identify an abnormality and often suggest the likelihood of cancer, but mammograms cannot diagnose cancer.
CT scans also use x-rays to create images. The images are more detailed because the CT scan looks at structures from different angles. The CT machine takes continuous pictures and reproduces them on a computer screen. The images can be viewed as thin sections or slices, making it easier to see inside structures.
Bone scans are images of the skeleton that highlight sites of bone metastases. To perform a radionuclide bone scan, the radiologist injects a radioactive substance into the blood, which is preferentially taken up by the actively dividing cancer cells. This area of increased cellular activity appears to a special camera outside the body as a “hot spot” in relation to the surrounding normal bone.
MRI scans create images using magnetic fields and radio waves. In an MRI scan, the body is exposed to strong magnetic fields while tiny pulses of radio waves are sent through the area of the body that is being studied. The radio waves passing through the different tissues disturb the magnetic field, causing signals to be emitted. The signals are processed by a computer and translated into an image. MRI scans may be better for detecting differences in soft tissues compared to a CT scan.
PET (positron emission tomography) scans are used to take computerized images of changes that occur in the tissues. The images are produced in color. For example, a radioactive substance is injected in the body. After a short time, the substance can be traced and watched to see how the body uses it. It can be helpful in spotting tumors that may not show up on other images. At times, PET and CT scans are combined to improve visualization and function in a specific area.
An ultrasound uses high-frequency sound waves to create images, much like a submarine uses sonar to identify objects in its path. Sound waves are bounced off interior structures and their reflection is used to create an image. Ultrasound is commonly used to detect certain abdominal tumors in the ovary, pancreas, and liver.
A definitive diagnosis of cancer ultimately requires a biopsy. A biopsy is a sample of tissue that is examined in a lab under a microscope by a pathologist. The biopsy will help determine if cancer is present, the type of cancer, and the tumor grade (how likely it is that the cancer will spread). A biopsy may be done as a procedure itself or during a surgery to remove suspicious tissue.
Types of biopsy include:
A superficial biopsy is used when a cell or tissue sample is easily accessible on a body surface. They rarely require a surgeon and can be done during a simple office-based procedure. Examples include a skin biopsy or Pap smear.
Endoscopy is the use of a thin, flexible tube equipped with a light source, video camera, and various surgical instruments. The scope allows the doctor to view suspicious tissue. During endoscopic biopsy, a doctor can take tissue samples in an area that looks suspicious.
Endoscopy is a generic term. Procedures are named for the specific areas of the body that are examined. For example, a colonoscopy is used to examine the large intestine while a bronchoscopy evaluates the lungs.
In a needle biopsy, a needle is inserted into a suspected tumor and a small sample of cells or tissue is withdrawn. There are 3 types of needle biopsies:
- Fine-needle aspiration —Fluid and cells from the tumor are sucked through a thin needle. This is commonly used to evaluate suspicious lumps in the breast.
- Core-needle biopsy —A larger needle is inserted, and a core of tissue is removed from the solid tumor.
- Stereotactic core-needle biopsy —A digital imaging camera is used to project an image of the tumor and determine its location. This process allows the doctor to position the needle in exactly the right place in order to get the desired sample.
If a tumor is inaccessible through either endoscopic or needle biopsy, a doctor may choose to do a surgical biopsy. A surgical biopsy may be excisional or incisional. In an excisional biopsy, the surgeon removes the entire tumor and some surrounding normal tissue. In an incisional biopsy, the doctor removes just a portion of the tumor. If cancer is present, the entire tumor may be removed right away or later during another surgery.
Cancer diagnosis. Merck Manual Professional version website. Available at: http://www.merckmanuals.com/professional/hematology-and-oncology/overview-of-cancer/cancer-diagnosis. Accessed January 29, 2021.
Diagnosis. National Cancer Institute website. Available at: http://www.cancer.gov/cancertopics/diagnosis-staging/diagnosis. Accessed January 29, 2021.
Tumor markers. National Cancer Institute website. Available at: http://www.cancer.gov/cancertopics/diagnosis-staging/diagnosis/tumor-markers-fact-sheet. Accessed January 29, 2021.
Last reviewed January 2021 by EBSCO Medical Review Board Last Updated: 1/29/2021