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What do cancer screening tests look for?

Screening tests are designed to check for early signs of cancer before symptoms appear. They are often a routine part of care and a proactive way to help stay on top of your health. Screening tests can help catch potential issues early when they may be easier to manage.

If your care team recommends a follow-up test, it often means they want more detail, not that something is necessarily wrong. Many follow-up tests come back normal, but they are an important part of the process to help your care team get a clearer picture of your health.

Here are some common screening tests and what they look for:

• Mammogram: Looks for changes in breast tissue that may suggest breast cancer, sometimes before a lump can be felt.
• Human papillomavirus (HPV) test: Checks for the virus linked to cervical cell changes that can lead to the development of cervical cancer.
• Colonoscopy: Can be used to find small growths (called polyps) or early signs of colorectal cancer. In some cases, polyps may be removed during the procedure. Not all polyps become cancer, and removal does not eliminate future risk, so follow-up testing may be recommended.
• Low-dose computed tomography (CT) scan: May be used to screen for lung cancer. If you currently smoke or have smoked in the past, your healthcare provider can help determine whether you meet current screening recommendations.
• Prostate-specific antigen (PSA) blood test: Can be used as part of a screening program for prostate cancer. The decision to have PSA testing is often made together with your healthcare provider, based on factors like your age, health and family history, and personal preferences.

Some screening tests can be done at home (like certain stool-based tests). These can be a convenient first step to screen for cancer. If a result is positive, unclear, or abnormal, it is important to follow up with a healthcare provider about next steps.

If you’re not sure which screening tests are relevant for you, there are simple ways to get started. You can explore options based on your age and health history in about 30 seconds with a personalized screening guide. You can also read Cancer screening: what it is and what it can tell you to learn more about different types of cancer screenings.

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What do cancer diagnostic tests look for?

Diagnostic tests help your doctor and care team get more details. These tests show what a finding or symptom could mean, where it is in the body, and whether it could be cancer.

Diagnostic testing usually works like a puzzle, where each test provides an important piece. Your care team uses those pieces together to build a clearer understanding of what is happening and to help decide what to do next.

Most diagnostic testing involves one or more of the following:

Imaging tests

These tests create images that help your care team “see” inside the body. Different types of imaging look for different things:

• CT scans: Use X-rays to produce detailed 3D images. They can help show whether a tumor may be present, its location, whether anything has changed or needs closer attention, and sometimes where to guide a biopsy.
• Magnetic resonance imaging (MRI): Uses radio waves and a strong magnet to create images, which can be helpful for looking at parts of the body like the brain, muscles, and other organs.
• Positron emission tomography (PET) or PET-CT: Uses a small amount of a radioactive sugar (called a tracer) that is injected into the bloodstream. The tracer is absorbed by cells in your body, and areas with unusual cell activity (like tumors) show up more clearly on images. This helps your care team identify areas that may need further attention. The amount of radiation in the tracer is low, and it leaves your body after the scan.

Biopsy tests

A biopsy is when a clinician removes a small sample of cells or tissue so it can be examined in a lab. Biopsies are not only used to diagnose cancer, but they can also help identify other conditions and provide more detailed information about what is going on inside the body.

A biopsy can give details that scans may not, such as:

• The cancer type (and sometimes the specific subtype)
• How different the cancer cells look compared to normal cells (the grade)
• Early signals about how the cells may behave over time
• Additional information that helps your care team understand next steps, including planning treatment or monitoring your condition

Your care team uses this information to guide treatment planning.

Learn more: Tissue and liquid biopsies explained.

Lab tests

Blood, urine, and other laboratory tests can measure substances in the body that may indicate the presence of cancer. Lab tests can provide clues, but they rarely tell the full story on their own.

For example, test results are often reviewed alongside other information, such as imaging, biopsy findings, and your overall health picture.

Biomarker testing

In some diagnostic situations, your care team may test tumor tissue or blood for biomarkers.

Biomarker testing looks for specific genes, proteins, or other signals that can provide more detailed information about a cancer. In some cases, these results may help guide treatment decisions by pointing to therapies that are more likely to work. If this is the case, it means there are actionable biomarkers. However, not all cancers have actionable biomarkers, and testing does not always lead to a change in treatment.

Learn more in What are cancer biomarkers and what is biomarker testing?