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Quick Facts

Diagnosis of Cancer

By The Manual's Editorial Staff,

How do doctors diagnose cancer?

Doctors may suspect you have cancer based on:

  • Your symptoms

  • A physical exam

  • Results from cancer screening tests (tests to look for cancer before you have symptoms)

To know for sure, doctors will do tests. They will diagnose (identify) your cancer using the test results.

Doctors will also do tests to see the stage of your cancer (stage I, stage II, stage III, or stage IV). Stages describe how big your cancer is and whether it has spread to other places in your body.

What tests can screen for cancer?

Screening tests are those your doctor does when you don't have any symptoms. Your doctor might suggest screening tests if you have a higher risk of having cancer based on your age, sex, family history, health, or lifestyle. Doctors use different screening tests for different cancers. Some screening tests can help save lives, but only certain screening tests are reliable.

Some common screening tests include:

  • A Pap test for cervical cancer

  • A mammogram (x-ray of your breast) for breast cancer

  • PSA test (prostate specific antigen) for prostate cancer

  • Tests of your stool (poop) or a colonoscopy for colon cancer

Doctors can do screening tests:

  • As part of your routine physical exam

  • At an office visit

  • During a procedure that has to be scheduled ahead of time

Even if a screening test is positive, doctors usually can’t tell for sure if you have cancer. Doctors will do more specific tests to know whether you have cancer.

What tests can diagnose cancer?

If doctors suspect cancer, they’ll usually do a test to take a picture of the inside of your body, such as an x-ray, ultrasound, or CT or MRI scan. To tell for sure, doctors will do:

  • A biopsy (take a sample of your tissue) and look at the sample under a microscope

Staging tests

When doctors diagnose your cancer, they’ll do tests to find out the stage. The stage tells them where and how large the cancer is. The stage also tells if the cancer has grown and spread into other parts of your body. Knowing the stage helps doctors decide the best treatment. Staging tests include:

  • Imaging tests, such as x-ray, CT and MRI scan, bones scans, and PET scans—your doctor will use some of these tests depending on the type of cancer

  • Biopsy from your tumor or tissues around your tumor

  • Blood tests to see if your liver, bones, and kidneys are working normally