A
Adjuvant — treatment given after primary treatment (usually surgery) to lower the chance of recurrence. Contrast with neoadjuvant, which is given before surgery.
AJCC staging — the American Joint Committee on Cancer’s system for describing how far a cancer has spread. Combines tumor size (T), lymph-node involvement (N), and distant spread (M) into stages 0–IV. Modern AJCC staging also incorporates tumor biology (grade, receptors).
Androgen receptor (AR) — a protein on or inside some breast cancer cells that binds the hormone testosterone. Tumors that express AR (the LAR subtype of TNBC) may respond to drugs that block androgen, similar to prostate cancer therapies.
Anthracycline — a class of chemotherapy drugs including doxorubicin (Adriamycin) and epirubicin. Effective in TNBC but can cause cardiac toxicity over time.
Antibody-drug conjugate (ADC) — a drug that combines a monoclonal antibody (which finds and binds a specific protein on cancer cells) with a chemotherapy payload, delivering the chemo directly to the cancer. TNBC examples: sacituzumab govitecan, trastuzumab deruxtecan.
Aromatase inhibitor — a class of endocrine therapy used in postmenopausal women with hormone receptor–positive breast cancer. Not used in TNBC because TNBC cells don’t have hormone receptors.
ASCENT — the clinical trial that established sacituzumab govitecan (Trodelvy) as a standard treatment for previously treated metastatic TNBC. Published 2021.
Atezolizumab (Tecentriq) — an immune checkpoint inhibitor previously used in first-line metastatic TNBC. The FDA approval for this indication was withdrawn in 2021; pembrolizumab is now the standard checkpoint inhibitor for TNBC.
Axillary dissection — surgery to remove most or all of the lymph nodes in the underarm. More extensive than sentinel lymph node biopsy; carries higher risk of lymphedema.
B
Biomarker — a measurable feature (a protein, a gene mutation, a tumor characteristic) used to predict response to a specific treatment or to estimate prognosis. PD-L1 expression and BRCA mutation status are biomarkers in TNBC.
Biopsy — removal of a small sample of tissue for examination under a microscope. The standard for diagnosing TNBC is a core needle biopsy guided by ultrasound or mammography.
Bone density scan (DEXA) — a low-radiation X-ray that measures bone strength. Used to monitor for osteoporosis, which can develop after chemo-induced menopause or aromatase inhibitor therapy.
BRCA1, BRCA2 — two genes whose normal job is to help repair certain kinds of DNA damage. Inherited mutations in either gene increase the lifetime risk of breast and ovarian cancers; about 70% of BRCA1-associated breast cancers are TNBC. PARP inhibitors are particularly effective in BRCA-mutated cancers.
C
Capecitabine (Xeloda) — an oral chemotherapy drug. Used after surgery for residual disease in TNBC (CREATE-X trial); also a single-agent option in metastatic disease.
Carboplatin — a platinum-based chemotherapy drug. Often included in neoadjuvant TNBC regimens, especially for BRCA-mutated cancers and for KEYNOTE-522-style protocols.
Cardiotoxicity — damage to the heart caused by certain treatments, especially anthracyclines. Monitored with echocardiograms before, during, and after treatment.
"Chemo brain" — common shorthand for the memory and concentration changes some patients notice during and after chemotherapy. Most improve over months to years.
Chemo-induced menopause — stopping of menstrual periods caused by chemotherapy damaging the ovaries. May be temporary in younger women or permanent in older ones.
Chemosensitive — likely to respond well to chemotherapy. TNBC is generally chemosensitive, which is one reason chemotherapy plays such a central role in treatment.
Combined Positive Score (CPS) — a pathology score that estimates the proportion of cells in a tumor specimen expressing PD-L1. A CPS of 10 or higher is the eligibility threshold for first-line pembrolizumab in metastatic TNBC.
Compression garment — specialized snug clothing worn on an arm or hand to manage or prevent lymphedema after axillary surgery.
Core needle biopsy — a biopsy that uses a hollow needle to remove small cylinders of tissue. The standard biopsy method for breast lesions; provides enough tissue for full receptor and biomarker testing.
CREATE-X — the trial that established adjuvant capecitabine for residual disease after neoadjuvant chemotherapy in TNBC. Published 2017.
Cyclophosphamide — a chemotherapy drug commonly used in combination with anthracyclines (the "C" in "AC" or "EC" regimens).
Cytotoxic chemotherapy — drugs that kill rapidly dividing cells — cancer cells, but also some normal cells (hair follicles, blood-cell precursors, gut lining), which is why hair loss, low blood counts, and digestive side effects are common.
D
DESTINY-Breast04 — the trial that established trastuzumab deruxtecan as a treatment option for HER2-low metastatic breast cancer, including a substantial fraction of historically TNBC tumors. Published 2022.
Doxorubicin (Adriamycin) — a widely used anthracycline chemotherapy drug. The "A" in "AC" regimens.
E
Echocardiogram — an ultrasound of the heart. Used to baseline and monitor heart function before, during, and after anthracycline chemotherapy.
Endocrine therapy — drugs that block or lower hormone signals (estrogen, progesterone) that fuel some breast cancers. Examples: tamoxifen, aromatase inhibitors. Not used in TNBC because TNBC cells lack hormone receptors.
Epirubicin — an anthracycline chemotherapy drug similar to doxorubicin; sometimes used as a substitute.
Eribulin (Halaven) — a chemotherapy drug used as a single agent in metastatic TNBC after prior treatment.
Estrogen receptor (ER) — a protein inside cells that binds estrogen. In hormone receptor–positive breast cancers, ER expression drives growth and is targeted by endocrine therapy. TNBC by definition has minimal or no ER expression.
F
FISH (fluorescence in situ hybridization) — a pathology test that counts how many copies of a specific gene a cancer cell has. Used in TNBC diagnosis to follow up ambiguous (IHC 2+) HER2 results.
Fine-needle aspiration (FNA) — a biopsy method that uses a thin needle to withdraw cells. Generally not sufficient for TNBC diagnosis because it doesn’t provide enough tissue for receptor testing; core needle biopsy is preferred.
G
Gemcitabine (Gemzar) — a chemotherapy drug used as a single agent or in combination in metastatic TNBC.
Germline mutation — a gene mutation present in every cell of a person’s body, inherited from a parent. Contrasted with somatic mutation (acquired only in tumor cells). Germline BRCA1/2 mutations have implications for the patient’s family members.
Grade (tumor grade) — how abnormal cancer cells look under the microscope. Grade 1 is well-differentiated (closer to normal cells, slower-growing); grade 3 is poorly differentiated (less normal, faster-growing). Most TNBCs are grade 3.
H
HER2 (human epidermal growth factor receptor 2) — a protein on the surface of some breast cancer cells that drives growth when overexpressed. HER2-positive cancers respond to drugs like trastuzumab (Herceptin). TNBC by definition has low or no HER2 expression.
HER2-low — a newer category for tumors that show some HER2 (IHC 1+ or 2+ without gene amplification) but not enough to be classified as HER2-positive. About half of historically TNBC tumors are HER2-low and may benefit from trastuzumab deruxtecan.
Histologic type — the structural pattern of the cancer cells under the microscope. Most TNBCs are invasive ductal carcinomas of "no special type."
Hospice — end-of-life care focused entirely on comfort. Distinct from palliative care, which can be delivered at any stage of illness alongside curative treatment.
Hypofractionated radiation — radiation given in fewer, larger doses over a shorter total time (typically 3–4 weeks instead of 5–6). Equally effective for most patients, with fewer skin side effects.
I
IHC (immunohistochemistry) — a pathology technique that stains tissue for specific proteins. The standard test for ER, PR, and HER2 status in breast cancer.
IHC score (0, 1+, 2+, 3+) — how strongly the IHC stain shows up. For HER2: 0 and 1+ are negative, 2+ is ambiguous (FISH testing follows), 3+ is positive.
Immune checkpoint inhibitor — a class of drugs that releases the brakes the immune system normally puts on itself, allowing T cells to attack cancer cells. Pembrolizumab (Keytruda) is the main checkpoint inhibitor used in TNBC.
Immunotherapy — treatment that uses the body’s immune system to fight cancer. In TNBC, immunotherapy currently means immune checkpoint inhibitors.
Infusion — a treatment given through a vein over a period of time (minutes to hours). Most TNBC chemotherapy and immunotherapy is given by infusion.
Interstitial lung disease (ILD) — inflammation and scarring of the lung tissue. A rare but serious side effect of trastuzumab deruxtecan that requires monitoring with imaging and prompt evaluation of any new cough or shortness of breath.
Invasive ductal carcinoma (IDC) — the most common type of breast cancer, including most TNBCs. "Invasive" means the cancer has grown beyond the milk duct where it began.
K
KEYNOTE-355 — the trial that established pembrolizumab plus chemotherapy as first-line treatment for PD-L1–positive metastatic TNBC. Published 2020.
KEYNOTE-522 — the trial that established pembrolizumab plus chemotherapy as the standard neoadjuvant regimen for high-risk early-stage TNBC. Published 2020 with updated outcomes 2022.
Ki-67 — a protein found in cells that are actively dividing. The percentage of cancer cells staining for Ki-67 (the "Ki-67 index") indicates how fast the tumor is growing. TNBC typically has a high Ki-67 index.
L
LAR subtype — Luminal Androgen Receptor; one of the molecular subtypes of TNBC, characterized by androgen receptor expression. Currently being investigated for treatment with androgen-blocking drugs.
Lumpectomy — surgery that removes the cancer plus a margin of surrounding tissue while preserving the rest of the breast. Typically followed by radiation. Long-term survival outcomes are equivalent to mastectomy for most patients.
Lymphedema — swelling, usually of an arm, caused by disrupted lymph drainage after axillary surgery and radiation. Early intervention with physical therapy and compression garments is much more effective than later intervention.
M
Mammography — X-ray imaging of the breast. Used for routine screening (annual or biennial) and for diagnostic evaluation when something is suspicious.
Mastectomy — surgery that removes all breast tissue from the affected side. Sometimes performed bilaterally (both sides), particularly in patients with BRCA1/2 mutations.
Metastatic — cancer that has spread beyond the original site to distant parts of the body. In TNBC, the most common metastatic sites are lungs, liver, bones, and brain.
MRI (magnetic resonance imaging) — imaging that uses magnetic fields and radio waves rather than X-rays. Used in breast cancer to assess tumor extent, look for additional lesions, and screen high-risk patients.
N
Neoadjuvant — treatment given before surgery, usually chemotherapy. Used to shrink the tumor and to assess how the cancer responds. Pathologic complete response after neoadjuvant therapy correlates with better long-term outcomes.
Neuropathy (peripheral neuropathy) — tingling, numbness, burning, or weakness in the fingers and toes, caused by chemotherapy damage to peripheral nerves. Most common with taxanes and platinums.
Neutrophil — a type of white blood cell that fights bacterial infection. Chemotherapy commonly lowers neutrophil counts (neutropenia), increasing infection risk; this is why fevers during chemo are a medical emergency.
O
Olaparib (Lynparza) — a PARP inhibitor approved for BRCA-mutated breast cancer in both metastatic (OlympiAD) and high-risk early-stage (OlympiA) settings.
OlympiA — the trial that established adjuvant olaparib for high-risk early-stage breast cancer in patients with germline BRCA1 or BRCA2 mutations. Published 2021.
OlympiAD — the trial that established olaparib for metastatic BRCA-mutated breast cancer. Published 2017.
Overall survival (OS) — in a clinical trial, how long patients live from a defined starting point (usually trial enrollment or randomization). The most patient-relevant trial endpoint.
P
Paclitaxel (Taxol) — a taxane chemotherapy drug widely used in TNBC. Often included in neoadjuvant regimens.
Palliative care — specialty medical care focused on relieving symptoms, side effects, and emotional burden of serious illness. Distinct from hospice; can be delivered at any stage alongside curative or life-prolonging treatment, and increasingly recommended early.
PARP inhibitor — a class of drugs that block an enzyme cancer cells need to repair certain kinds of DNA damage. Particularly effective in BRCA-mutated cancers, which already have impaired DNA repair. Examples: olaparib, talazoparib.
Pathologic complete response (pCR) — no residual cancer cells found in the breast or lymph nodes when the surgical specimen is examined after neoadjuvant therapy. Strongly correlated with better long-term outcomes in TNBC.
Pathologist — a physician specialist who examines tissue under the microscope and orders the molecular tests that classify a cancer.
Patient navigator — a trained staff member at many cancer centers who helps patients schedule appointments, understand insurance, coordinate care across specialists, and find resources. Free at most centers; ask for one early.
PD-L1 — a protein some cancer cells display on their surface that lets them evade attack by immune T cells. Pembrolizumab and similar drugs block PD-L1 (or its receptor PD-1) and "release the brakes" on the immune response.
Pembrolizumab (Keytruda) — an immune checkpoint inhibitor used in PD-L1–positive metastatic TNBC (KEYNOTE-355) and as part of neoadjuvant therapy in high-risk early-stage TNBC (KEYNOTE-522).
Phase 1 / 2 / 3 trial — the three main stages of clinical drug testing. Phase 1 is small and tests safety and dose; phase 2 expands to test how well the drug works; phase 3 is large and randomized, comparing the new treatment against current standard.
Port (chemo port, port-a-cath) — a small device implanted under the skin, with a catheter into a large vein, used to give chemotherapy and draw blood without repeatedly accessing arm veins.
Progesterone receptor (PR) — a protein inside cells that binds progesterone. In hormone receptor–positive breast cancers, PR expression contributes to growth signaling. TNBC by definition has minimal or no PR expression.
Progression-free survival (PFS) — in a clinical trial, the time from a defined starting point until the cancer grows or the patient dies. Often used as an interim endpoint when overall-survival data isn’t yet mature.
R
Radiation therapy — treatment that uses high-energy beams to kill cancer cells. Used after lumpectomy nearly always, after mastectomy depending on tumor size and lymph-node involvement, and sometimes for symptom control in metastatic disease.
Randomized trial — a clinical trial in which patients are assigned by chance to one of two or more treatment arms. The strongest design for comparing treatments, because it minimizes the risk that differences between groups are caused by something other than the treatment.
Receptor — a protein on or inside a cell that recognizes and binds a specific signaling molecule (a hormone, a growth factor, a drug). The cell responds to whatever the receptor binds.
Reconstruction — surgery to rebuild the appearance of a breast after mastectomy. Can use implants, the patient’s own tissue, or a combination; performed at the time of mastectomy or later.
Reproductive endocrinologist — a fertility specialist. Cancer-experienced reproductive endocrinologists handle fertility preservation (egg or embryo freezing) for patients facing chemotherapy.
Residual cancer burden (RCB) — a standardized measurement of how much cancer remains in the breast and lymph nodes after neoadjuvant therapy. RCB is graded 0 (pCR), I, II, or III; higher categories correlate with worse long-term outcomes.
S
Sacituzumab govitecan (Trodelvy) — an antibody-drug conjugate that targets Trop-2 on the surface of TNBC cells and delivers a chemotherapy payload directly into them. Established by ASCENT for previously treated metastatic TNBC.
Scalp cooling cap — a cap worn during chemotherapy infusions to lower scalp temperature, reducing (though not eliminating) chemotherapy-induced hair loss.
"Scanxiety" — common shorthand for the anxiety many cancer survivors experience in the days and weeks before each surveillance scan. A real and validated phenomenon, not a personal failing.
Sentinel lymph node biopsy — surgery to remove the first one or two lymph nodes most likely to contain cancer cells if the cancer has spread. Less extensive than full axillary dissection; lower lymphedema risk.
Single-agent chemotherapy — chemotherapy given as one drug at a time rather than in combination. Often used in metastatic TNBC because it’s better tolerated than combination chemotherapy over the long run.
Staging — the process of determining how far a cancer has spread. See AJCC staging.
T
Talazoparib (Talzenna) — a PARP inhibitor approved for BRCA-mutated metastatic breast cancer. Established by EMBRACA.
Tamoxifen — a drug that blocks estrogen receptors. Standard endocrine therapy for hormone receptor–positive breast cancer; not used in TNBC because TNBC cells don’t have estrogen receptors.
Taxane — a class of chemotherapy drugs that interferes with cell division. Includes paclitaxel and docetaxel; widely used in TNBC.
Trastuzumab (Herceptin) — a monoclonal antibody that targets HER2. Standard treatment for HER2-positive breast cancer; not used in classic TNBC because TNBC cells don’t have enough HER2.
Trastuzumab deruxtecan (Enhertu) — an antibody-drug conjugate combining trastuzumab with a chemotherapy payload. Used in HER2-positive disease and now also in HER2-low disease, which includes about half of historically TNBC tumors. Established by DESTINY-Breast04 for the HER2-low indication.
Triple-negative — refers to cancers that test negative for all three of the standard breast cancer molecular targets: estrogen receptor (ER), progesterone receptor (PR), and HER2. Defines TNBC.
TNM staging — the cornerstone of AJCC staging. T describes tumor size and local extent, N describes lymph-node involvement, M describes distant spread.
Trop-2 — a protein found on the surface of most TNBC cells; the target of sacituzumab govitecan.
V
Vinorelbine (Navelbine) — a chemotherapy drug used as a single agent in metastatic TNBC.
Last reviewed: 2026-05-15. This page is information only, not medical advice. Definitions are intentionally simplified for general readers; the precise clinical meaning of any term may vary by context. If a definition here conflicts with what your care team has told you about your specific situation, defer to your team.