Acute: Refers to symptoms that start and worsen quickly but do not last over a long period of time
Benign: Refers to a tumor that is not cancerous. The tumor does not usually invade nearby tissue or spread to other parts of the body.
Biopsy: The removal of a small amount of tissue for examination under a microscope. Other tests can suggest that cancer is present, but only a biopsy can make a definite diagnosis. Learn more about what to expect during a biopsy .
Bone marrow: The soft, spongy tissue found in the center of large bones where blood cells are formed
Cancer: A group of more than 100 different diseases that can begin almost anywhere in the body; characterized by abnormal cell growth and the ability to invade nearby tissues. Learn more about the basics of cancer .
Carcinoma: Cancer that starts in skin or tissues that line the inside or cover the outside of internal organs
Cells: The basic units that make up the human body
Chemoprevention: The use of natural, synthetic (made in a laboratory), or biologic (from a living source) substances to reverse, slow down, or prevent the development of cancer. Learn more about chemoprevention .
Chemotherapy: The use of drugs to kill cancer cells. Learn more about chemotherapy. 
Chronic: Refers to a disease or condition that persists, often slowly, over a long period of time
Imaging test: A procedure that creates pictures of internal body parts, tissues, or organs to make a diagnosis, plan treatment, check whether treatment is working, or observe a disease over time
In situ: In place. Refers to cancer that has not spread to nearby tissue (also called non-invasive cancer).
Invasive cancer: Cancer that has spread outside the layer of tissue in which it started and has the potential to grow into other tissues or parts of the body (also called infiltrating cancer)
Laboratory test: A procedure that evaluates a sample of blood, urine, or other substance from the body to make a diagnosis, plan treatment, check whether treatment is working, or observe a disease over time
Leukemia: A cancer of the blood. Leukemia begins when normal white blood cells change and grow uncontrollably.
Localized cancer: Cancer that is confined to the area where it started and has not spread to other parts of the body
Lymph nodes: Tiny, bean-shaped organs that help fight infection, which is a part of the lymphatic system
Lymphatic system: A network of small vessels, ducts, and organs that carry fluid to and from the bloodstream and body tissues. Through the lymphatic system, cancer can spread to other parts of the body.
Lymphoma: A cancer of the lymphatic system. Lymphoma begins when cells in the lymph system change and grow uncontrollably and may form a tumor.
Malignant: Refers to a tumor that is cancerous. It may invade nearby healthy tissue or spread to other parts of the body.
Mass: A lump in the body
Metastasis: The spread of cancer from the place where the cancer began to another part of the body; cancer cells can break away from the primary tumor and travel through the blood or the lymphatic system to the lymph nodes, brain, lungs, bones, liver, or other organs.
Oncologist: A doctor who specializes in treating people with cancer. The five main types of oncologists are medical, surgical, radiation, gynecologic, and pediatric oncologists. Learn more about the types of oncologists .
Oncology: The study of cancer
Pathologist: A doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease
Polyp: A growth of normal tissue that usually sticks out from the lining of an organ, such as the colon
Precancerous: Refers to cells that have the potential to become cancerous. Also called pre-malignant.
Predisposition: A tendency to develop a disease that can be triggered under certain conditions. For example, a genetic predisposition to cancer increases a person's risk of developing cancer, it is not certain that the person will develop it. Learn more about genetics .
Primary cancer: Describes the original cancer
Prognosis: Chance of recovery; a prediction of the outcome of a disease. Learn more about survival statistics  used to estimate a patient’s prognosis.
Sarcoma: A cancer that develops in the tissues that support and connect the body, such as fat and muscle. Learn more about sarcoma .
Screening: The process of checking whether a person has a disease or has an increased chance of developing a disease when the person has no symptoms
Secondary cancer: Describes either a new primary cancer (a different type of cancer) that develops after treatment for the first type of cancer, or cancer that has spread to other parts of the body from the place where it started (see metastasis, above)
Stage: A way of describing cancer, such as where it is located, whether or where it has spread, and whether it is affecting the functions of other organs in the body. Learn more about staging .
Tumor: A mass formed when normal cells begin to change and grow uncontrollably. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).