Oncology Terms Glossary

Understanding cancer terminology can help you better communicate with your healthcare team and understand your diagnosis and treatment options.

Written by: Oncol.net editorial team | Reviewed by the Oncol.net editorial team | Last updated: October 9, 2026

How to Use This Oncology Glossary

This glossary explains, in plain English, the oncology terms and abbreviations that appear most often in clinic letters, pathology reports and blood test results. Search for a term or jump to a letter below; each entry links to a fuller guide where one exists.

The terms patients ask about most are about staging (stage, TNM, grade), treatment timing (adjuvant, neoadjuvant) and blood counts during chemotherapy (ANC, nadir, febrile neutropenia). For quick look-ups, see the common abbreviations table.

A

Adjuvant Therapy (AD-joo-vant)

Also known as: Adjuvant treatment

Treatment given after the primary treatment to lower the risk that the cancer will come back. Adjuvant therapy may include chemotherapy, radiation therapy, hormone therapy, targeted therapy, or immunotherapy.

Adenocarcinoma (A-deh-noh-kar-sih-NOH-mah)

Cancer that begins in glandular (secretory) cells. Glandular cells are found in tissue that lines certain internal organs and makes and releases substances in the body, such as mucus, digestive juices, or other fluids.

Alkylating Agent (AL-kih-LAY-ting)

A type of chemotherapy drug that works by adding an alkyl group to the DNA of cancer cells, preventing them from dividing and causing them to die. Examples include cyclophosphamide, cisplatin, and carboplatin.

Anaplastic (A-nah-PLAS-tik)

A term used to describe cancer cells that divide rapidly and have little or no resemblance to normal cells. Anaplastic cancers tend to be aggressive.

Angiogenesis (AN-jee-oh-JEH-neh-sis)

The formation of new blood vessels. Tumors need angiogenesis to grow beyond a certain size because they need a blood supply to bring oxygen and nutrients.

Absolute Neutrophil Count (ANC)

The number of neutrophils, the white blood cells that fight bacterial infection, in a microlitre of blood. It is calculated as total white count × (% neutrophils + % bands) ÷ 100. Normal is about 1,500–8,000/µL; below 1,500 is neutropenia and below 500 is severe neutropenia.

Anemia (uh-NEE-mee-uh)

Also known as: Anaemia

A lower-than-normal level of hemoglobin or red blood cells, usually below 12 g/dL in women or 13 g/dL in men. During cancer treatment it commonly causes tiredness, breathlessness and a fast heartbeat.

B

Benign (beh-NINE)

Not cancerous. Benign tumors may grow larger but do not spread to other parts of the body. They are usually not life-threatening.

Biomarker (BY-oh-MAR-ker)

Also known as: Tumor marker, Molecular marker

A biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease. Biomarkers may be used to see how well the body responds to treatment.

Biopsy (BY-op-see)

The removal of cells or tissues for examination by a pathologist. The pathologist may study the tissue under a microscope or perform other tests on the cells or tissue.

Bone Marrow

The soft, sponge-like tissue in the center of most bones. It produces white blood cells, red blood cells, and platelets.

C

Carcinoma (kar-sih-NOH-mah)

Cancer that begins in the skin or in tissues that line or cover internal organs. This is the most common type of cancer.

Chemotherapy (KEE-moh-THAYR-uh-pee)

Also known as: Chemo

Treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. May be given by mouth, injection, or infusion.

Clinical Trial

A type of research study that tests how well new medical approaches work in people. These studies test new methods of screening, prevention, diagnosis, or treatment of a disease.

Complete Response (CR)

Also known as: Complete remission

The disappearance of all signs of cancer in response to treatment. This does not always mean the cancer has been cured.

Complete Blood Count (CBC)

Also known as: Full blood count (FBC), blood counts

A routine blood test that measures white blood cells (including the ANC), red blood cells and hemoglobin, and platelets. It is checked before each cycle of chemotherapy to decide whether treatment can go ahead safely.

CTCAE (Common Terminology Criteria for Adverse Events)

The National Cancer Institute’s standard scale for grading side effects from 1 (mild) to 5 (death related to the side effect). For example, neutropenia, diarrhea and radiation dermatitis are all graded on CTCAE.

D

Differentiation

Describes how much or how little tumor tissue looks like the normal tissue it came from. Well-differentiated cancer cells look more like normal cells and tend to grow and spread more slowly than poorly differentiated or undifferentiated cancer cells.

Dose-limiting Toxicity (DLT)

Side effects of a drug or treatment that are serious enough to prevent an increase in dose or level of that treatment.

E

Epithelial (eh-pih-THEE-lee-ul)

Refers to cells that line the internal and external surfaces of the body. Epithelial cancers (carcinomas) are the most common type of cancer.

F

Febrile Neutropenia

Also known as: Neutropenic fever

A fever of 100.4°F (38°C) or higher in someone whose neutrophil count is very low (usually an ANC below 500/µL). It is a medical emergency during chemotherapy and is treated with antibiotics as soon as possible.

G

Grade

A description of a tumor based on how abnormal the cancer cells look under a microscope and how quickly the tumor is likely to grow and spread. Low-grade cancer cells look more like normal cells and tend to grow slowly.

I

Immunotherapy (IH-myoo-noh-THAYR-uh-pee)

Treatment that uses certain parts of a person's immune system to fight diseases such as cancer. This can include stimulating your own immune system to work harder or using man-made immune system proteins.

In Situ (in SY-too)

In its original place. For example, carcinoma in situ is cancer that has not spread to nearby tissue (also called stage 0 cancer).

M

Malignant (mah-LIG-nant)

Cancerous. Malignant tumors can invade and destroy nearby tissue and spread to other parts of the body.

Metastasis (meh-TAS-tah-sis)

Plural: Metastases

The spread of cancer from one part of the body to another. A tumor formed by cells that have spread is called a metastatic tumor or a metastasis.

Monoclonal Antibody (MAH-noh-KLOH-nul AN-tih-BAH-dee)

A type of protein made in the laboratory that can bind to substances in the body, including cancer cells. Used in both cancer treatment and diagnosis.

N

Neoadjuvant Therapy (NEE-oh-AD-joo-vant)

Treatment given before the main treatment. Examples include chemotherapy, radiation therapy, and hormone therapy given before surgery to shrink a tumor.

Neutropenia (noo-troh-PEE-nee-uh)

A condition in which there is a lower-than-normal number of neutrophils (a type of white blood cell). This increases the risk of infection.

Nadir (NAY-der)

The lowest point that blood counts reach after a dose of chemotherapy, usually 7–14 days after treatment for most regimens. Infection risk is highest around the nadir.

O

Oncogene (ON-koh-jeen)

A gene that has the potential to cause cancer. When mutated or expressed at high levels, oncogenes can transform a normal cell into a tumor cell.

Oncologist (on-KAH-loh-jist)

A doctor who specializes in treating cancer. Types include medical oncologists (chemotherapy), radiation oncologists (radiation therapy), and surgical oncologists (surgery).

P

Palliative Care (PAL-ee-uh-tiv)

Care given to improve the quality of life of patients who have a serious or life-threatening disease. The goal is to prevent or treat symptoms and side effects, not to cure the disease.

Pathology (pah-THAH-loh-jee)

The study of disease. In cancer care, pathology involves examining tissues and cells under a microscope to diagnose cancer and determine its type and grade.

Primary Tumor

The original tumor; the place where cancer began. Cancer cells can spread from the primary tumor to other parts of the body and form new (secondary) tumors.

Prognosis (prog-NOH-sis)

The likely outcome or course of a disease; the chance of recovery or recurrence.

Peripheral Neuropathy

Also known as: CIPN

Damage to the nerves outside the brain and spinal cord, causing numbness, tingling, burning or weakness, usually starting in the fingers and toes. Chemotherapy-induced peripheral neuropathy (CIPN) is common with taxanes, platinum drugs and vinca alkaloids.

Platelets

Also known as: Thrombocytes, PLT

Small blood cells that help blood clot. A normal count is about 150,000–400,000/µL. A low count (thrombocytopenia) increases bleeding and bruising.

R

Radiation Therapy (RAY-dee-AY-shun)

Also known as: Radiotherapy

The use of high-energy radiation from x-rays, gamma rays, neutrons, protons, and other sources to kill cancer cells and shrink tumors.

Remission

A decrease in or disappearance of signs and symptoms of cancer. In partial remission, some but not all signs have disappeared. In complete remission, all signs have disappeared.

Radiation Dermatitis (der-muh-TY-tis)

Skin inflammation in the area treated with radiation therapy, ranging from redness and dry peeling (grade 1) to moist peeling and, rarely, ulceration (grade 4).

S

Stage

The extent of cancer in the body, including tumor size and whether it has spread. Staging helps determine the best treatment approach and prognosis.

Systemic Therapy

Treatment that travels through the bloodstream to reach cells throughout the body. Includes chemotherapy, hormone therapy, targeted therapy, and immunotherapy.

T

Targeted Therapy

A type of treatment that uses drugs or other substances to identify and attack specific cancer cells without harming normal cells.

TNM System

A system to describe the amount and spread of cancer: T describes tumor size, N describes spread to nearby lymph nodes, and M describes metastasis.

Tumor

An abnormal mass of tissue that results when cells divide more than they should or do not die when they should. Tumors may be benign (not cancer) or malignant (cancer).

Thrombocytopenia (throm-boh-sy-toh-PEE-nee-uh)

A platelet count below the normal range (usually below 150,000/µL). Below about 50,000/µL bleeding precautions are tightened, and below 10,000–20,000/µL a platelet transfusion may be given.

Common Oncology Abbreviations

Abbreviations you are likely to see in clinic letters, treatment plans and lab reports. Ask your team if you meet one that is not listed.

Abbreviation	Meaning
ANC	Absolute neutrophil count — infection-fighting white cells
CBC / FBC	Complete (full) blood count
Hgb / Hb	Hemoglobin — oxygen-carrying protein in red cells
PLT	Platelets — clotting cells
WBC	White blood cell count
CTCAE	Common Terminology Criteria for Adverse Events — side-effect grading scale
CIPN	Chemotherapy-induced peripheral neuropathy
FN	Febrile neutropenia — fever with low neutrophils
G-CSF	Granulocyte colony-stimulating factor, e.g. filgrastim
TNM	Tumour, Nodes, Metastasis — staging system
ECOG / PS	Performance status — how much daily activity you can manage, scored 0–5
CR / PR / SD / PD	Complete response, partial response, stable disease, progressive disease
NED	No evidence of disease
Tx / Rx	Treatment / prescription
Dx	Diagnosis
Mets	Metastases — cancer that has spread
RT / XRT	Radiotherapy (radiation therapy)
IO	Immuno-oncology (immunotherapy)
PICC	Peripherally inserted central catheter — a long IV line in the arm
IHC	Immunohistochemistry — staining tissue to identify proteins

Frequently Asked Questions

What does ANC mean on a blood test?

ANC stands for absolute neutrophil count, the number of infection-fighting neutrophils per microlitre of blood. Normal is about 1,500 to 8,000/µL. Below 1,500 is called neutropenia and below 500 is severe, which is when infection risk is highest during chemotherapy.

What is the difference between adjuvant and neoadjuvant therapy?

Neoadjuvant therapy is given before the main treatment, usually surgery, often to shrink the tumour. Adjuvant therapy is given after the main treatment to lower the chance of the cancer coming back.

What does a CTCAE grade mean?

CTCAE is the National Cancer Institute’s scale for grading side effects. Grade 1 is mild, grade 2 moderate, grade 3 severe, grade 4 life-threatening and grade 5 death related to the side effect. Your team uses the grade to decide whether to continue, delay or adjust treatment.

What does nadir mean in chemotherapy?

The nadir is the lowest point your blood counts reach after a chemotherapy dose, usually 7 to 14 days afterwards for most regimens. It is when infection risk is highest, so a fever of 100.4°F (38°C) or higher at any time during treatment needs urgent care.

What do the letters T, N and M mean in cancer staging?

T describes the size and extent of the main tumour, N whether the cancer has reached nearby lymph nodes, and M whether it has spread (metastasised) to distant parts of the body. Together they are combined into an overall stage, usually from I to IV. See our TNM staging guide.