Screening basics

What cancer screening is, how it differs from testing when you have symptoms, and what the possible benefits and harms are.

Rosa: Hi, I'm Rosa. Screening means checking for cancer before you have any signs. Let's look at how it works, and the good and the not so good parts.

Cancer screening is a test for people who feel well and have no signs of cancer. The goal is to find cancer early, when it is often smaller and easier to treat. Some screening tests can even find growths before they turn into cancer, so they can be removed.

Screening is different from testing when you have symptoms. If you have a new lump, bleeding that is not normal, a cough that will not go away, or weight loss you cannot explain, do not wait for your next screening test. Call your doctor. You need a diagnostic test, which is a test to find out what is causing the problem.

Screening has real benefits, but it also has possible harms. A false alarm is when a test looks worrying but there is no cancer. False alarms can lead to more tests, worry, and sometimes a biopsy. A biopsy is when a doctor takes a small piece of tissue to look at under a microscope.

Screening can also find small cancers that would never have caused problems. This is called overdiagnosis. It can lead to treatment a person did not need. This is one reason why experts recommend screening only for certain ages and risk levels.

Expert groups, like the U.S. Preventive Services Task Force and the American Cancer Society, study the research and write screening advice. Sometimes their advice is a little different. When that happens, talk with your doctor about what fits you best.

Your personal risk matters. Family history, past cancer, smoking, and some health conditions can mean you should start earlier or be tested more often. Make sure your doctor knows your full health and family history.

Screening test

A test for people with no symptoms. It looks for cancer or for changes that could become cancer.

Diagnostic test

A test done because you have a symptom or an abnormal screening result. It helps find the cause.

False alarm

A result that looks abnormal, but more testing shows no cancer. Doctors call this a false positive.

Missed cancer

No test is perfect. A screening test can sometimes miss a cancer. This is why you should still report new symptoms.

Overdiagnosis

Finding a cancer that would never have grown or caused harm. It can lead to treatment that was not needed.

Shared decision

A talk with your doctor about the good and bad sides of a test, so you can choose what is right for you.

• Ask your doctor which screening tests are right for your age and health.
• Tell your doctor about cancer in your parents, brothers, sisters, and children.
• Keep a list of the screening tests you have had and their dates.
• Ask what happens next if a result is not normal.
• Call your doctor about new symptoms, even if your last screening test was normal.

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.