What biomarker tests are recommended for Triple-Negative Breast Cancer

Biomarker Testing for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a particularly aggressive form of breast cancer that lacks three key receptors: estrogen receptor (ER), progesterone receptor (PR), and HER2. Because these cancers don't respond to hormone therapy or HER2-targeted drugs, biomarker testing becomes especially important to identify other treatment options.

Standard Biomarker Tests for TNBC

According to NCCN Guidelines for Invasive Breast Cancer, your care team will recommend biomarker testing to look for specific DNA mutations and proteins that can guide treatment decisions. Here are the key tests:

1. PD-L1 Testing (Immune Checkpoint Protein)

PD-L1 (programmed death ligand 1) is an immune protein that cancer cells sometimes use to hide from your immune system. If your cancer expresses PD-L1, you may be eligible for immunotherapy combined with chemotherapy—treatments designed to activate your immune system to fight the cancer cells more effectively.

2. Tumor Mutational Burden (TMB-H)

This test counts the number of mutations in your tumor DNA. When there are 10 or more mutations per million base pairs (called TMB-high or TMB-H), it can predict better response to immune checkpoint inhibitor therapies like pembrolizumab.

3. Microsatellite Instability (MSI-H) or Mismatch Repair Deficiency (dMMR)

These tests look for defects in your cancer cells' DNA repair systems. If present, they may indicate eligibility for specific immunotherapies (pembrolizumab or dostarlimab).

4. BRCA1/BRCA2 Mutations (Germline and Somatic)

• Germline testing: Checks if you inherited a BRCA mutation from your parents
• Somatic testing: Checks if mutations exist only in the tumor cells

BRCA mutations are particularly important in TNBC because they open the door to PARP inhibitor therapy (olaparib or talazoparib), which targets cancer cells with defective DNA repair. According to NCCN Guidelines, these are Category 1 preferred treatments for patients with BRCA mutations.

5. Other Actionable Mutations

Your oncologist may test for additional mutations that can be targeted:

• NTRK fusions: Can be treated with larotrectinib, entrectinib, or repotrectinib
• RET fusions: Can be treated with selpercatinib
• PALB2 mutations: May indicate eligibility for olaparib

6. Tumor Markers (Blood Tests)

Blood tests may measure proteins like:

• CEA (carcinoembryonic antigen)
• CA 15-3
• CA 27.29

Important note: These tumor markers alone are not reliable for detecting cancer, but elevated levels can help track how well treatment is working.

Testing Methods

According to NCCN Guidelines, biomarker testing uses several approaches:

• NGS (Next-Generation Sequencing): Reads your tumor's DNA to identify mutations
• IHC (Immunohistochemistry): Uses stains to detect specific proteins
• FISH: Identifies specific gene changes
• Liquid biopsy: Tests circulating tumor DNA (ctDNA) in your blood—useful when tissue samples are limited

Why This Matters for TNBC

Because triple-negative breast cancers don't respond to hormone therapy or HER2-targeted treatments, biomarker testing is your roadmap to finding which targeted therapies or immunotherapies might work best for YOUR specific cancer. Each mutation or protein finding can point toward different treatment options.

Questions to Ask Your Oncologist

1. Which biomarker tests have been done on my tumor, and which ones are still pending?
2. Do I have any mutations (BRCA, NTRK, RET, PALB2) that would make me eligible for targeted therapy?
3. What is my PD-L1 status and TMB score, and what do these mean for my treatment options?
4. If my initial tests don't show actionable mutations, are there other tests you recommend?
5. Should I have repeat testing if my cancer progresses, since biomarkers can change over time?

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