What Is Genetic Testing? A Complete Guide

Genetic testing is a medical test that examines your DNA — the biological instruction set you inherited from your parents — to look for specific changes, also called variants or mutations. Some of these changes can increase your risk of developing certain diseases, including various types of cancer.

In the context of hereditary cancer screening, genetic testing focuses on genes that, when altered, are associated with a significantly higher likelihood of developing certain cancers over a person’s lifetime. Understanding whether you carry such a change can help you and your healthcare team make informed decisions about prevention, early detection, and treatment.

How Genetic Testing Works

Modern genetic testing typically requires only a small biological sample — often saliva collected at home or a blood draw at a clinic. The sample is sent to a certified laboratory where technologists use advanced sequencing technology to read specific portions of your DNA.

The lab compares your DNA sequence against known reference sequences. When a difference is detected, scientists assess whether the change is benign (harmless), pathogenic (disease-associated), or a variant of uncertain significance (VUS), meaning its impact is not yet fully understood.

Types of Genetic Tests

There are several types of genetic tests, each serving different purposes:

• Single-gene testing: Examines one specific gene, often used when a known family variant has already been identified.
• Panel testing: Analyzes multiple genes at once. Hereditary cancer panels may examine 20 to 80 or more genes associated with increased cancer risk.
• Whole exome or genome sequencing: Reads most or all of your DNA. This is more commonly used in research or for rare conditions rather than routine cancer screening.

For hereditary cancer risk assessment, multi-gene panel testing is the most common approach. It provides a comprehensive look at the genes most frequently linked to hereditary cancer syndromes while remaining cost-effective and clinically actionable.

What Genetic Testing Can and Cannot Tell You

Genetic testing can reveal whether you carry a gene change that is associated with increased cancer risk. However, it is important to understand its limitations:

• A positive result does not mean you will definitely develop cancer. It means your risk may be higher than average, and enhanced screening or preventive measures may be recommended.
• A negative result does not guarantee you will never develop cancer. Most cancers are not hereditary, and factors like environment, lifestyle, and chance also play roles.
• A variant of uncertain significance (VUS) means the lab found a change but does not yet know whether it is harmful. These results may be reclassified as scientists learn more.

Who May Benefit from Genetic Testing

Clinical guidelines, such as those from the National Comprehensive Cancer Network (NCCN), suggest that genetic testing may be particularly valuable for people with certain risk factors. These include a strong family history of cancer, a personal history of cancer diagnosed at a young age, or ancestry from populations where certain gene changes are more common.

You can learn more about specific risk factors in our article on who should consider genetic testing.

The Role of Genetic Counseling

Genetic testing is most valuable when paired with genetic counseling. A licensed genetic counselor can help you understand what testing is appropriate, interpret your results in the context of your personal and family history, and discuss what the findings mean for you and your relatives.

Whether you are considering testing for the first time or have already received results you want to understand better, a genetic counselor is a valuable partner in the process. Learn more about what to expect in our guide to the genetic testing process.