Understanding Genetic Testing for Cancer: What Your Results Mean

Understanding Genetic Testing for Cancer: What Your Results Mean

If you or a loved one has been diagnosed with cancer, you’ve likely heard the term “genetic testing.” It can feel overwhelming. But understanding your test results can empower you and your care team to make the most informed decisions about your treatment and future health.

This guide will walk you through the different types of tests, what the results mean, and how this knowledge can directly impact your care.

The Two Types of Genetic Tests: Germline vs. Somatic

Think of your body’s genetics as having two libraries.

Germline testing looks at the library you were born with—the genes you inherited from your parents. This is done using a sample of your blood or saliva. These tests look for changes, often called mutations, that you’ve had your entire life. Finding a mutation here can explain why a cancer developed and is crucial for understanding risk for you and your family. This is often called "hereditary" or "inherited" cancer testing.

Somatic testing looks at the library of the cancer itself. This test is performed on a sample of the tumor removed during a biopsy or surgery. It looks for genetic changes that the cancer cells acquired over your lifetime. These mutations weren’t inherited; they happened by chance. This information is vital because it helps doctors choose treatments, like targeted therapies or immunotherapies, that specifically attack cancer cells with those mutations.

In short: germline testing tells you about your inherited risk, while somatic testing tells your doctor about the cancer’s unique weaknesses.

Common Genetic Panels: What Are They Looking For?

Doctors often order tests that look at multiple genes at once, called a panel. Here are some of the most common ones you might hear about.

The BRCA Gene Panel

You’ve likely heard of BRCA1 and BRCA2. These genes are your body’s master tumor suppressors—they act like skilled repair crews that fix damaged DNA in your cells. A harmful mutation in either gene means this repair crew isn’t working properly, allowing damaged cells to grow into cancer.

• What it means: A pathogenic mutation in BRCA1 or BRCA2 significantly increases the lifetime risk of breast, ovarian, prostate, and pancreatic cancers.
• Why it matters for treatment: This is a powerful example of how a germline test result directly guides therapy. If you have a BRCA mutation, your cancer may respond exceptionally well to a class of drugs called PARP inhibitors. These drugs exploit the cancer’s existing DNA repair weakness to destroy it.

Lynch Syndrome Panel

This panel looks at a different set of DNA repair genes (MLH1, MSH2, MSH6, PMS2, and EPCAM). A mutation in any of these genes causes Lynch syndrome.

• What it means: Lynch syndrome raises the risk for colorectal, endometrial (uterine), stomach, ovarian, and other cancers, often at a younger age than average.
• Why it matters for treatment: Cancers caused by Lynch syndrome often have a specific signature called MSI-H (microsatellite instability-high). This makes them visible to your immune system. As a result, these cancers can be highly responsive to immunotherapy drugs, which unleash your body’s immune cells to fight the cancer.

Multi-Gene Panels

Technology now allows doctors to test for dozens of cancer-risk genes simultaneously. A multi-gene panel casts a wide net, looking for mutations in many genes beyond just BRCA and those linked to Lynch syndrome.

This is especially helpful if your personal or family history of cancer is strong but doesn’t perfectly fit a well-known syndrome. It provides a more complete picture of your inherited cancer risk.

Deciphering Your Results: Pathogenic, VUS, and Benign

Your genetic test report will categorize the findings. Here’s what those terms actually mean.

Pathogenic (or Likely Pathogenic) Variant This means a harmful mutation was found. Think of it as a confirmed typo in the gene’s instruction manual that prevents it from working correctly. This result provides a clear explanation for your cancer risk and guides next steps for management, prevention, and testing for family members.

Benign (or Likely Benign) Variant This is a normal difference in the gene—like a harmless spelling variation that doesn’t affect how the word is understood. The gene works perfectly fine. This is a negative result and is reassuring.

Variant of Uncertain Significance (VUS) This is the most frustrating result for many people. A VUS means a change was found in the gene, but scientists don’t yet have enough evidence to know if it’s harmful (pathogenic) or harmless (benign). It’s a “we don’t know yet.”

• Important: A VUS is not considered a positive test result. It should not be used to make decisions about surgery, treatment, or screening. Doctors will manage your care based on your personal and family history alone. Over time, as more people are tested, many VUS results are reclassified as either benign or pathogenic.

When Should You Get Tested?

Genetic testing isn’t for everyone. Doctors typically recommend it based on "red flags" in your personal or family history, such as:

• Cancer diagnosed at a young age (under 50)
• Several close relatives with the same type of cancer or related cancers (e.g., breast and ovarian)
• A single person with multiple different cancers
• Rare cancers (like ovarian or pancreatic cancer)
• A known hereditary cancer syndrome in your family

The best first step is to meet with a genetic counselor. They are experts who can review your history, discuss the pros and cons of testing, help you choose the right test, and explain your results in depth.

How Genetic Testing Affects Your Treatment

Your genetic results can open doors to powerful, precise treatments.

1. Targeted Therapies: Somatic testing can find a specific mutation in your tumor that can be targeted with a pill. For example, mutations in genes like EGFR, ALK, or BRAF have corresponding drugs designed to block them.
2. Immunotherapy: As mentioned with Lynch syndrome, tumors with certain genetic signatures (like MSI-H) are more likely to respond to immunotherapy.
3. Prevention and Screening: A germline test result can lead to a personalized plan to catch cancer early or even prevent it. This could mean starting mammograms or colonoscopies earlier, having them more often, or considering risk-reducing surgeries.
4. Informing Your Family: A positive germline test result means your blood relatives (children, siblings, parents) have a 50/50 chance of having the same mutation. This knowledge allows them to get tested and take proactive steps to protect their health.

What You Can Do Next

1. Talk to Your Doctor: Ask if genetic testing is appropriate for you based on your diagnosis and family history.
2. Request a Genetic Counselor: They are your dedicated guide through this complex process. Your oncology team can refer you.
3. Bring Your Family History: Before any appointment, write down your family health history—who had cancer, what type, and how old they were at diagnosis. This is the most valuable tool for assessing your risk.
4. Ask Questions: Don’t be afraid to ask, “What does this test mean for my treatment?” and “What does it mean for my family?”

Understanding your genetic test results turns fear of the unknown into a clear plan of action. It is one of the most powerful tools in modern oncology, tailoring your care to you and your unique cancer.