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Diagnosing Cancer

How is cancer diagnosed?

Certain tests are needed to find out if a person has cancer or if some other problem (such as an infection) is causing cancer symptoms. Sometimes tests need to be repeated if the person's condition changes, if a sample of collected tissue or fluid was not of good quality, or if an abnormal test result needs to be confirmed.

The correct diagnosis is needed to guide treatment. The tests you have depend on your symptoms and the type of cancer your healthcare provider suspects. Your provider will do a complete medical history and physical exam. A biopsy is often needed to diagnose cancer.

  • Tumor biopsy.  For a biopsy, a tiny piece of tissue is taken out of the tumor and tested in a lab. This might be done with a needle or during surgery. Biopsies are often needed for a diagnosis since they give the most exact exam and testing of tissue. 

Other tests that check for cancer or see how far it has spread often include:

  • Complete blood count. A small needle is used to take blood out of a vein in the arm or hand. This blood test measures the size, number, and maturity of different blood cells in your blood. Abnormal cells may be a sign of cancer. Changes in the normal number, size, and maturity of cells may also be a sign of a cancer.

  • Bone marrow aspiration, biopsy, or both. This procedure involves taking out a small amount of bone marrow fluid (aspiration) or solid bone marrow tissue (called a core biopsy). This is most often done from the back of the hip bones. The samples removed are examined for the number, size, and maturity of blood cells or abnormal cells.

  • Spinal tap (lumbar puncture). This procedure is done to test the fluid around the spine and brain for pressure or infection and find any abnormal cells. A thin needle is put between the bones of the lower back, into the spinal canal. This is the area around the spinal cord. The pressure in the spinal canal and brain can then be measured. A small amount of cerebral spinal fluid (CSF) can be taken out and sent for testing to see if there's an infection or other problem. CSF is the fluid that bathes and cushions the brain and spinal cord.

  • Ultrasound (sonography). This is an imaging test that uses sound waves and a computer to make images of blood vessels, tissues, and organs. A small wand is moved across the skin over the part of the body to be checked. Ultrasounds are used to look at organs as they work, and to look at how blood flows through vessels. Tumors in the stomach, liver, and kidneys can often be seen with an ultrasound.

  • Bone scans. A radioactive dye is put into the blood through a vein and absorbed by bone. Scans then show where the dye collects. These "hotspots" might be tumors or other bone abnormalities.

  • X-ray. This imaging test uses beams of radiation to make images of tissues, bones, and organs on film. X-rays may be taken of any part of the body to look for a tumor.

  • CT scan. This is an imaging test that uses X-rays and a computer to make detailed images of the inside of the body. A CT scan shows details of the bones, muscles, fat, and organs. The person lies on a thin table that slides through a ring-shaped scanner to do this test.

  • PET-CT (positron emission tomography and CT scans). A radioactive sugar is put in the blood before this test. It collects in areas of active cells. Then the CT scan makes detailed pictures of tissues and organs while the PET scan shows abnormal cell activity. A more complete image is provided by combining these tests. The person lies on a narrow table that slowly moves through a series of ring-shaped scanners to do this test.

  • MRI. An MRI uses large magnets, radiofrequencies, and a computer to make detailed images of organs and structures inside the body. This test doesn't use X-rays. The table the person lies on slides through a long, thin, tube-like scanner. Some people have trouble being inside the narrow scanner.

  • Blood tests. Blood tests are used to look at a person's electrolytes, liver function, kidney function, presence of infection, tumor markers (chemicals released by a tumor), or genetic testing. Genetic counseling may be advised for families that are found or believed to have an inherited risk of cancer. A needle is used to get the blood for this test from a vein in the arm or hand.

  • Surgery. Surgery may be needed to do a biopsy, remove tumors, remove organs affected by disease, and to look for tumors that may not be found with imaging tests. There are many kinds of surgery that can be done.

Online Medical Reviewer: Jessica Gotwals RN BSN MPH
Online Medical Reviewer: Sabrina Felson MD
Online Medical Reviewer: Todd Gersten MD
Date Last Reviewed: 5/1/2023
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