What's the difference between genomic and genetic testing? How would that help think about treatment options? What...

Understanding Genomic vs. Genetic Testing for Colorectal Cancer

Great question—this distinction is really important for your care, and I'm glad you're asking about it early.

The Key Difference

Genetic testing looks at genes you were born with—mutations inherited from your parents that are in every cell of your body. These are called germline mutations.

Genomic testing analyzes the mutations that developed specifically in your tumor cells over time. These are called somatic mutations—they're unique to your cancer and weren't inherited.

According to the LEAF Webinar "The Latest Tests for Personalized Cancer Care," this distinction matters significantly. As expert Tony Magliocco explains: "A germ cell tells you not only about yourself and your whole body... your children might be affected with it as well." But for treating your tumor, somatic mutations take priority because they're what's actually driving your specific cancer cells to grow.

Why Both Matter for Your Treatment

Somatic (tumor) mutations are more important for immediate treatment decisions because they directly target what's fueling your cancer. However, germline (inherited) mutations matter because they:

• May guide you toward specific therapies (like PARP inhibitors if you have BRCA mutations)
• Affect screening recommendations for you and family members
• Influence your overall cancer risk

Common Colorectal Cancer Mutations to Know

Here are key acronyms you should be familiar with:

KRAS - One of the most common mutations in colorectal cancer (found in ~40% of cases). Traditionally considered "undruggable," but newer targeted therapies are emerging.

TP53 - A tumor suppressor gene frequently mutated in colorectal cancer. Its presence can affect prognosis and treatment response.

APC - Often the initiating mutation in colorectal cancer development. Important for understanding your cancer's biology.

BRAF - Found in about 5-10% of colorectal cancers. BRAF-mutant tumors may respond to specific targeted therapies.

MSI/dMMR - Microsatellite Instability or deficient Mismatch Repair. This is increasingly important because it can predict response to immunotherapy drugs.

BRCA1/BRCA2 - Germline mutations that increase colorectal cancer risk and may influence treatment options.

EGFR - While more common in lung cancer, EGFR status matters in colorectal cancer for certain targeted therapies.

How This Guides Your Treatment Thinking

According to the LEAF Webinar "Self-Advocacy in the Era of Precision Medicine," you should ask your doctor: "What additional tests should I get to possibly identify new treatment options and personalize my care?"

Here's the practical framework:

1. Get comprehensive genomic profiling of your tumor early. This identifies somatic mutations that might respond to targeted drugs or immunotherapy.

2. Ask about germline testing, especially if you have:

   • Family history of colorectal or other cancers
   • Early-age diagnosis
   • Specific tumor characteristics (like MSI-high)

3. Understand the "weighting": Somatic mutations in your tumor get priority for treatment selection, but germline results inform your long-term health strategy and family screening.

What You Should Do Now

The LEAF Webinar "How Do You Choose Your Diagnostics" emphasizes that "every cancer patient should get standard tests for their disease." For colorectal cancer, this means:

• Ask your oncologist: "Can I get a comprehensive genomic profile of my tumor?"
• Request testing for MSI/dMMR status (increasingly standard)
• Ask about liquid biopsy options (blood tests that can detect tumor DNA)
• Get a copy of your complete test report
• Consider genetic counseling to interpret results, especially if germline mutations are found

Important Note

Don't assume one test is enough. As noted in the LEAF Webinar "Self-Advocacy in the Era of Precision Medicine," some patients get a false sense of security after initial genetic testing. You may benefit from multiple types of testing—genomic profiling, liquid biopsies, and potentially other advanced tests—to get the most complete picture of your cancer's biology.

Bottom line: Somatic mutations drive your immediate treatment decisions, while germline mutations inform your broader health strategy. Both deserve attention, and you should advocate for comprehensive testing early in your journey.

Would you like me to explain any of these mutations in more detail, or help you prepare questions for your oncologist about testing?