How Cancer Is Diagnosed

X-rays use low doses of radiation to create pictures of the inside of your body.

X-rays use low doses of radiation to create pictures of the inside of your body.

Credit: iStock

If you have a symptom or a screening test result that suggests cancer, your doctor must find out whether it is due to cancer or some other cause. The doctor may start by asking about your personal and family medical history and do a physical exam. The doctor also may order lab tests, imaging tests (scans), or other tests or procedures. You may also need a biopsy, which is often the only way to tell for sure if you have cancer.

This page covers tests that are often used to help diagnose cancer. Depending on the symptoms you have, you may have other tests, too. To learn more about how specific cancers are diagnosed, see the PDQ® cancer treatment summaries for adult and childhood cancers. These summaries include detailed information about and pictures of diagnostic tests and procedures for each specific type of cancer.

  • Lab Tests
  • Imaging Tests
  • Biopsy
  • After Cancer Is Diagnosed

Lab Tests


High or low levels of certain substances in your body can be a sign of cancer. So, lab tests of your bloodurine, or other body fluids that measure these substances can help doctors make a diagnosis. However, abnormal lab results are not a sure sign of cancer. Learn more about laboratory tests and how they are used to diagnose cancer.

Some lab tests involve testing blood or tissue samples for tumor markers. Tumor markers are substances that are produced by cancer cells or by other cells of the body in response to cancer. Most tumor markers are made by normal cells and cancer cells but are produced at much higher levels by cancer cells. Learn more about tumor markers and how they are used to diagnose cancer.

Imaging Tests


Imaging tests create pictures of areas inside your body that help the doctor see whether a tumor is present. These pictures can be made in several ways:

CT Scan

CT scan uses an x-ray machine linked to a computer to take a series of pictures of your organs from different angles. These pictures are used to create detailed 3-D images of the inside of your body.

Sometimes, you may receive a dye or other contrast material before you have the scan. You might swallow the dye, or it may be given by a needle into a vein. Contrast material helps make the pictures easier to read by highlighting certain areas in the body.

During the CT scan, you will lie still on a table that slides into a donut-shaped scanner. The CT machine moves around you, taking pictures. Learn more about CT scans and how they are used to diagnose cancer.


An MRI uses a powerful magnet and radio waves to take pictures of your body in slices. These slices are used to create detailed images of the inside of your body, which can show the difference between healthy and unhealthy tissue.

When you have an MRI, you lie still on a table that is pushed into a long, round chamber. The MRI machine makes loud thumping noises and rhythmic beats.

Sometimes, you might have a special dye injected into your vein before or during your MRI exam. This dye, called a contrast agent, can make tumors show up brighter in the pictures.

Nuclear scan

nuclear scan uses radioactive material to take pictures of the inside of the body. This type of scan may also be called radionuclide scan.

Before this scan, you receive an injection of a small amount of radioactive material, which is sometimes called a tracer. It flows through your bloodstream and collects in certain bones or organs.

During the scan, you lie still on a table while a machine called a scanner detects and measures the radioactivity in your body, creating pictures of bones or organs on a computer screen or on film.

After the scan, the radioactive material in your body will lose its radioactivity over time. It may also leave your body through your urine or stool.

Bone Scan

Bone scans are a type of nuclear scan that check for abnormal areas or damage in the bones. They may be used to diagnose bone cancer or cancer that has spread to the bones (also called metastatic bone tumors).

Before this test, a very small amount of radioactive material is injected into your vein. As it travels through the blood, the material collects in abnormal areas in the bone. Areas where the material collects show up on pictures taken by a special scanner. These areas are called “hot spots.”

PET scan

PET scan is a type of nuclear scan that makes detailed 3-D pictures of areas inside your body where glucose is taken up. Because cancer cells often take up more glucose than healthy cells, the pictures can be used to find cancer in the body.

Before the scan, you receive an injection of a tracer called radioactive glucose. During the scan, you will lie still on a table that moves back and forth through a scanner.


An ultrasound exam uses high-energy sound waves that people cannot hear. The sound waves echo off tissues inside your body. A computer uses these echoes to create pictures of areas inside your body. This picture is called a sonogram.

During an ultrasound exam, you will lie on a table while a tech slowly moves a device called a transducer on the skin over the part of the body that is being examined. The transducer is covered with a warm gel that makes it easier to glide over the skin.


X-rays use low doses of radiation to create pictures inside your body. An x-ray tech will put you in position and direct the x-ray beam to the correct part of your body. While the images are taken, you will need to stay very still and may need to hold your breath for a second or two.



In most cases, doctors need to do a biopsy to diagnose cancer. A biopsy is a procedure in which the doctor removes a sample of tissue. A pathologist looks at the tissue under a microscope and runs other tests to see if the tissue is cancer. The pathologist describes the findings in a pathology report, which contains details about your diagnosis. Pathology reports play an important role in diagnosing cancer and helping decide treatment options. Learn more about pathology reports and the type of information they contain.

The biopsy sample may be obtained in several ways:

With a needle: The doctor uses a needle to withdraw tissue or fluid. This method is used for bone marrow aspirationsspinal taps, and some breast, prostate, and liver biopsies.

With endoscopy: The doctor uses a thin, lighted tube called an endoscope to examine areas inside the body. Endoscopes go into natural body openings, such as the mouth or anus. If the doctor sees abnormal tissue during the exam, he will remove the abnormal tissue along with some of the surrounding normal tissue through the endoscope.

Examples of endoscopy exams include:

  • Colonoscopy, which is an exam of the colon and rectum. In this type of exam, an endoscope goes through the anus, allowing the doctor to examine the rectum and colon. If the doctor sees polyps, she will remove them and send them to a lab for testing.
  • Bronchoscopy, which is an exam of the tracheabronchi, and lungs. In this type of exam, an endoscope goes through the mouth or nose and down the throat.

With surgery: A surgeon removes an area of abnormal cells during an operation. Surgery may be excisional or incisional.

In an excisional biopsy, the surgeon removes the entire area of abnormal cells. Often some of the normal tissue around these cells is also removed.

In an incisional biopsy, the surgeon removes just part of the abnormal area.

Some biopsies may require a sedative or anesthesia

Sedatives are medicine that help you relax and stay very still or sleep during a biopsy.

Anesthesia keeps you from feeling pain. It refers to drugs or other substances that cause you to lose feeling or awareness. There are three types of anesthesia:

  • Local anesthesia, which causes loss of feeling in one small area of the body
  • Regional anesthesia, which causes loss of feeling in a part of the body, such as an arm or leg
  • General anesthesia, which causes loss of feeling and a complete loss of awareness that seems like a very deep sleep

After Cancer Is Diagnosed


If the biopsy and other tests show that you have cancer, you may have more tests to help your doctor plan treatment. For instance, your doctor will need to figure out the stage of your cancer. For some cancers, knowing the grade of the tumor or risk group that you fall into are important for deciding on the best treatment. Your tumor may also be tested further for other tumor or genetic markers.