What are genomic sequencing, genetic testing, and biomarker testing

Understanding Genomic Sequencing, Genetic Testing, and Biomarker Testing

These are three related but distinct approaches to understanding cancer at the molecular level. Let me break down each one:

Genomic Sequencing

Genomic sequencing is the process of reading the complete genetic code (DNA) of cancer cells to identify mutations and changes. Think of it like reading an instruction manual letter-by-letter to find all the typos and errors.

What it does:

• Maps out thousands of genetic variations in tumor cells
• Identifies mutations that drive cancer growth
• Can reveal new mutations that might be targetable with specific drugs
• Provides a comprehensive "genetic fingerprint" of the cancer

Example: Sequencing might reveal that a lung cancer has a specific EGFR mutation, which tells doctors the cancer will likely respond to EGFR-targeted drugs.

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Genetic Testing

Genetic testing typically refers to testing YOUR inherited DNA (not the cancer's DNA) to see if you carry mutations that increase cancer risk.

What it does:

• Checks for inherited gene mutations you were born with
• Identifies if you have higher lifetime cancer risk
• Helps determine if family members should be screened
• Informs prevention and surveillance strategies

Common examples:

• BRCA1/BRCA2 testing (breast and ovarian cancer risk)
• Lynch syndrome testing (colorectal cancer risk)
• PTEN testing (multiple cancer types)

Important distinction: This is about YOUR germline (inherited) DNA, not your tumor's DNA.

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Biomarker Testing

Biomarkers are measurable characteristics of cancer cells that help predict how the cancer will behave and which treatments might work best. They're like "flags" that oncologists look for.

What it does:

• Identifies specific proteins, mutations, or other features in tumor cells
• Predicts treatment response and prognosis
• Guides treatment selection
• Can be detected through various tests (sequencing, immunohistochemistry, blood tests)

Common biomarkers include:

• Hormone receptors (ER/PR in breast cancer) - indicates if hormone therapy will work
• HER2 status - shows if targeted HER2 drugs are appropriate
• PD-L1 expression - predicts response to immunotherapy
• BRAF, KRAS, EGFR mutations - specific mutations that respond to targeted drugs
• Microsatellite instability (MSI) - indicates immunotherapy eligibility
• Tumor mutational burden (TMB) - predicts immunotherapy response

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How They Work Together

According to NCCN Guidelines, modern cancer care often uses all three approaches:

1. Genetic testing → Identifies if you have inherited risk factors
2. Genomic sequencing → Reads your tumor's DNA to find mutations
3. Biomarker testing → Identifies specific features that guide treatment selection

Real-world example: A patient with breast cancer might have:

• Genetic testing showing no BRCA mutations (low inherited risk)
• Genomic sequencing revealing an HER2 amplification in the tumor
• Biomarker testing confirming HER2-positive status
• Result: HER2-targeted therapy (like trastuzumab) becomes the treatment focus

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Why This Matters for Your Care

The American Cancer Society and NCCN Guidelines recommend that most cancer patients have biomarker testing on their tumor to guide treatment decisions. This helps oncologists:

• Select the most effective drugs for YOUR specific cancer
• Avoid ineffective treatments
• Identify clinical trial opportunities
• Predict how well treatment might work

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Questions to Ask Your Oncologist

If you're facing a cancer diagnosis, consider asking:

1. "What biomarker testing has been done on my tumor, and what did it show?"
2. "Are there any genetic tests I should have to understand my inherited cancer risk?"
3. "Based on my biomarkers, what treatment options are most likely to work for me?"
4. "Are there any additional genomic tests that would help guide my treatment?"
5. "Will my insurance cover these tests?"

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This information is for educational purposes only. Always consult your healthcare team for personalized medical advice and decisions.