Glossary

Cancer terminology glossary

Plain-language definitions of common cancer terms. Written for patients and caregivers, not clinicians. For more depth, see our patient guides.

A

Adjuvant therapy: Treatment given after the main treatment (usually surgery) to lower the chance the cancer returns. Examples include adjuvant chemotherapy or adjuvant radiation.
Antibody-drug conjugate (ADC): A monoclonal antibody chemically linked to a chemotherapy payload. The antibody targets cancer cells, delivering the payload directly. Examples: trastuzumab deruxtecan, sacituzumab govitecan, enfortumab vedotin.

B

Biomarker: A measurable characteristic of cancer cells (a protein, gene mutation, or pattern) that helps predict response to a specific therapy. Examples: HER2 in breast, EGFR in lung, MSI in colorectal.
Biopsy: A procedure that removes cells or tissue so a pathologist can examine them for cancer. May be needle, core, excisional, or endoscopic.
BRCA1 / BRCA2: Genes whose mutations substantially raise the risk of breast, ovarian, pancreatic, and prostate cancers. Patients with BRCA mutations may respond to PARP inhibitors.

C

CAR-T therapy: Chimeric Antigen Receptor T-cell therapy. Your own T-cells are collected, genetically modified to recognize your cancer, expanded, and infused back. Approved for specific leukemias, lymphomas, and multiple myeloma.
Checkpoint inhibitor: A drug that blocks proteins (like PD-1, PD-L1, or CTLA-4) that cancer uses to hide from the immune system. Examples: pembrolizumab, nivolumab, atezolizumab, ipilimumab.
Chemotherapy: Drugs that kill rapidly dividing cells, including cancer cells. Can be given by IV infusion or by mouth. Systemic — treats cancer throughout the body.
Clinical trial: A research study testing a new therapy or intervention in patients. Phases 1 (safety), 2 (efficacy signal), 3 (vs standard of care), 4 (post-approval monitoring).
Complete response (CR): Disappearance of all detectable cancer after treatment. Not synonymous with cure — microscopic disease may remain.
CT scan: Computed tomography imaging. X-rays taken from many angles and combined to produce cross-section views. Used for staging, monitoring response, and surveillance.
Cytoreductive surgery: Surgery aimed at removing as much visible cancer as possible, even when complete removal isn't feasible. Used in ovarian, appendiceal, and some other cancers.

D

DCIS: Ductal Carcinoma In Situ. Non-invasive breast cancer cells confined to the milk ducts. Stage 0. Often highly curable.
Dose-dense / dose-intense: Chemotherapy given on a shorter schedule (e.g., every 2 weeks instead of every 3) to maintain cancer suppression. Requires close monitoring of blood counts.
Dosimetry / dose-volume histogram: In radiation therapy, the calculated distribution of radiation dose across the tumor and surrounding tissues. How much tissue gets what dose.

E

ECOG Performance Status: A 0–5 scale describing how much a patient's illness affects daily life. 0 = fully active; 4 = completely disabled. Used for trial eligibility.
ER / PR: Estrogen Receptor and Progesterone Receptor. Breast cancer cells are tested for these; positive status means hormonal therapy is typically effective.

F

First-line / second-line / third-line: Order of treatment when one therapy fails or is not tolerated. First-line = the first treatment tried. Second-line = what you go to if first-line stops working. And so on.

G

Grade (tumor grade): How abnormal cancer cells look under a microscope. Grade 1 (well-differentiated, slow-growing) to Grade 3 (poorly-differentiated, aggressive). Different from stage.

H

HCC: Hepatocellular Carcinoma — the most common primary liver cancer.
HER2: A protein on breast and some other cancer cells. HER2-positive tumors respond to HER2-targeted therapies like trastuzumab.
Hormone receptor-positive (HR+): Breast cancer with estrogen and/or progesterone receptors present. Usually treated with hormonal therapy.
HPV (Human Papillomavirus): Virus linked to cervical cancer, most head-and-neck cancers, and some anal cancers. HPV-positive head-and-neck cancers have better prognosis than HPV-negative.

I

Immune-related adverse event (irAE): Side effect from immunotherapy caused by the activated immune system attacking healthy tissue. Can affect skin, gut, lungs, thyroid, liver, and other organs.
Immunotherapy: Drugs that activate or modify the immune system to attack cancer. Checkpoint inhibitors (pembrolizumab, nivolumab) and CAR-T are examples.
In situ: Cancer cells confined to the layer of tissue they started in, without invasion. Stage 0.

L

Lead time: The amount of time between early detection (e.g., by screening) and when the cancer would have been clinically diagnosed without screening. Not the same as added life.
Liquid biopsy: Blood-based test that detects tumor DNA or cells circulating in the bloodstream. Used when tissue biopsy is difficult or to monitor response.
Lymph node: Small bean-shaped organ that filters lymph. Cancers often spread to nearby (regional) lymph nodes first. 'Node-positive' is a key staging marker.

M

Maintenance therapy: Lower-intensity treatment continued after main treatment to delay recurrence. Common with PARP inhibitors in ovarian cancer and lenalidomide in myeloma.
Metastasis (metastatic): Spread of cancer from its origin to distant parts of the body. Metastatic (Stage IV) cancer is treated systemically.
MRD (Minimal Residual Disease): Cancer cells remaining after treatment, below the threshold of imaging. Measured in blood cancers via sensitive PCR/flow tests. MRD-negative status is a good prognostic sign.
MSI / MMR: Microsatellite Instability / Mismatch Repair status. MSI-High or dMMR tumors often respond to immune checkpoint inhibitor therapy.
Mutation (somatic vs germline): Somatic = mutation in the tumor only, acquired during life. Germline = inherited mutation present in every cell. BRCA1/2 can be either. Germline has implications for family.

N

NCI-designated Cancer Center: A U.S. cancer center recognized by the National Cancer Institute for research and clinical excellence. 71 centers across 37 states.
NED (No Evidence of Disease): No detectable cancer on imaging and exam. Same as complete response when used after treatment.
Neoadjuvant chemotherapy (NACT): Chemotherapy given before surgery to shrink the tumor. Response to NACT provides prognostic info not available after upfront surgery.
Neoadjuvant therapy: Treatment given before the main treatment (usually surgery) to shrink the tumor or kill micrometastatic disease.

O

Oligometastatic: Metastatic cancer with a limited number of distant lesions (typically 1–5). Often treated more aggressively with local therapy (surgery or radiation) to each lesion.
Oncologist: A physician specializing in cancer. Medical, radiation, surgical, gynecologic, hematologic, and pediatric are subspecialties.
Overall survival (OS): Length of time from diagnosis (or start of treatment) until death from any cause. The gold-standard endpoint in trials.

P

Palliative care: Specialized medical care focused on symptom management and quality of life. Not the same as hospice — palliative care can start at diagnosis and is often given alongside active treatment.
PARP inhibitor: A class of targeted therapy that exploits DNA-repair defects in BRCA-mutated and HRD-positive cancers.
Partial response (PR): Significant reduction in cancer (typically ≥30% decrease in target lesion size) after treatment, but not complete disappearance.
Pathology report: A formal document from the pathologist describing the cancer's type, grade, size, margins, node involvement, and molecular features.
PD-L1: A protein on cancer cells that can indicate whether the tumor may respond to PD-1/PD-L1 immune checkpoint inhibitors.
Performance status (PS): A scale (ECOG 0–5 or Karnofsky 100–0) describing how active a patient is. Affects eligibility for clinical trials and aggressive treatments.
Phase 1 / 2 / 3 / 4 trial: Stages of clinical testing: safety (1), efficacy signal (2), head-to-head vs standard (3), post-approval monitoring (4).
Primary / metastatic (site): Primary = where the cancer started (e.g., primary breast cancer). Metastatic site = where it has spread (e.g., liver metastasis from breast cancer).
Prognosis: The likely course of disease. Based on population averages, not individual predictions.
Progression-free survival (PFS): Length of time during and after treatment when the cancer does not grow. Used as a trial endpoint for faster results than overall survival.

R

Radiation therapy: Treatment using ionizing radiation to damage cancer DNA. External beam, brachytherapy, proton therapy, and stereotactic (SBRT/SRS) are variants.
Radiofrequency ablation (RFA): A needle inserted into a tumor delivers heat energy to destroy cancer cells. Used for some liver, lung, and kidney cancers.
RECIST: Response Evaluation Criteria in Solid Tumors. Standardized rules for measuring whether tumors shrink, stay stable, or grow on imaging during a clinical trial.
Recurrence: Return of cancer after a period of remission. Can be local, regional, or distant.
Remission: A period during which cancer is not detectable. Partial remission = some cancer remains but tumor shrunk; complete remission = no cancer detected (not necessarily cured).

S

SEER: Surveillance, Epidemiology, and End Results — the NCI's database of U.S. cancer incidence and survival statistics.
Sentinel lymph node biopsy (SLNB): Surgery that removes only the first lymph node(s) a cancer would drain to, testing those for spread. Less invasive than full lymph-node dissection.
Staging (TNM): Tumor (T), Node (N), Metastasis (M) — the AJCC staging system. Combines into Stage I–IV.
Standard of care: The currently accepted best treatment for a particular cancer, based on evidence and guidelines.
Stereotactic body radiation therapy (SBRT): Highly focused, high-dose radiation delivered in a small number of sessions. Used for some lung cancers, early prostate, liver, and oligometastatic disease.
Systemic therapy: Treatment that affects the whole body — chemotherapy, targeted therapy, hormonal therapy, or immunotherapy.

T

Targeted therapy: Drugs designed to act on a specific molecular feature of cancer cells (e.g., a mutated protein), sparing normal cells more than chemotherapy.
TMB (Tumor Mutational Burden): Number of mutations per megabase of tumor DNA. TMB-High tumors often respond to immune checkpoint inhibitors — pembrolizumab is approved across TMB-H solid tumors regardless of type.
Tumor board: A multidisciplinary meeting where oncologists, surgeons, radiation oncologists, pathologists, and radiologists review a case and agree on a treatment plan. Standard at academic centers.

W

Watch and wait: Active surveillance without immediate treatment, used when cancer is slow-growing and treatment side effects outweigh benefits. Common in some low-grade lymphomas, low-risk prostate cancer, and low-risk CLL.