What is TNBC (triple-negative breast cancer)?

What the “triple-negative” part means

In most breast cancers, the cancer cells themselves carry one or more of three markers on or inside them. These markers serve as therapeutic targets:

1. Estrogen receptor (ER) — a protein inside the cancer cell that binds estrogen; when present, the hormone fuels the cell’s growth.
2. Progesterone receptor (PR) — similarly, a protein inside the cancer cell that binds progesterone and drives growth.
3. HER2 — a growth-signaling protein on the surface of the cancer cell that, when overexpressed, drives the cell to divide rapidly.

When a tumor biopsy is tested, pathologists examine the cancer cells specifically for these markers. If the cancer cells test positive for any of them, doctors can use targeted therapies: endocrine therapy (such as tamoxifen or aromatase inhibitors) for hormone receptor–positive cancers, or HER2-targeted agents such as trastuzumab (Herceptin) for HER2-positive disease.

In TNBC, the cancer cells test negative for all three markers.

Clinical characteristics

Without those targets on the cancer cells, treatment relies on surgery, radiation, and cytotoxic chemotherapy. TNBC tends to be chemosensitive and often responds to neoadjuvant (pre-surgery) chemotherapy; achieving a pathologic complete response (no residual cancer found at surgery) correlates with better long-term outcomes.

TNBC is biologically aggressive: higher proliferation rate, higher histologic grade, and a greater tendency to metastasize early — particularly to the lungs, liver, and brain. Recurrence risk is concentrated in the first 3–5 years after diagnosis. Five-year survival is lower than for hormone receptor–positive or HER2-positive subtypes, though absolute numbers vary substantially by stage at diagnosis.

Epidemiology

TNBC accounts for roughly 10–15% of breast cancers. It is more common in women under 40, in Black women, and in patients carrying a BRCA1 mutation (BRCA1-associated breast cancers are TNBC approximately 70% of the time).

Treatment options beyond chemotherapy

Several non-chemotherapy options exist for specific subsets of TNBC patients. Each works by targeting a different feature of the cancer cells:

• Immune checkpoint inhibitors — pembrolizumab (Keytruda) is used in combination with chemotherapy for PD-L1–positive metastatic TNBC and for high-risk early-stage disease. PD-L1 is a protein some TNBC cells display that lets them evade immune attack; this drug blocks that evasion.
• Antibody-drug conjugates (ADCs) — sacituzumab govitecan (Trodelvy) binds to Trop-2, a protein on the surface of most TNBC cells, and delivers a chemotherapy payload directly into them; it is used in metastatic TNBC after prior therapy. Trastuzumab deruxtecan (Enhertu) is an option for tumors whose cells show low HER2 expression.
• PARP inhibitors — olaparib and talazoparib are used in patients with germline BRCA1 or BRCA2 mutations, which leave the cancer cells unable to repair certain types of DNA damage.

Eligibility for each depends on tumor biology, genetic testing, and disease stage. Patients who remain disease-free past the 3–5 year window have a lower risk of late recurrence than those with hormone receptor–positive disease, where recurrences can occur a decade or more after initial treatment.

Last reviewed: 2026-05-30. This page is information only, not medical advice. Always discuss decisions about diagnosis or treatment with a qualified clinician.