Glossary of Cancer Terms



A unit of measure for radiation. It stands for radiation absorbed dose.


A general term for any form of radiant energy emission. Various forms of radiation can be used to diagnose or treat disease.

Radiation oncologist

A doctor who specializes in the use of radiation to treat cancer.

Radiation physicist

A person trained to ensure that the radiation machine delivers the right amount of radiation to the treatment site. Assists the radiation oncologist and dosimetrist in the design, planning, and calculation of the proper dose for radiation treatment.

Radiation therapist

A health professional who specializes in the use of radiation to treat cancer.

Radiation therapy

The use of high-energy radiation from x-rays, cobalt, radium, and other sources to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external beam radiation therapy) or from materials called radioisotopes. Radioisotopes produce radiation and are placed in or near the tumor or in the area near the cancer cells. This type of radiation treatment is called internal radiation therapy, implant radiation, interstitial radiation, or brachytherapy. Systemic radiation therapy uses a radioactive substance, such as a radiolabeled monoclonal antibody, that circulates throughout the body.

Radical mastectomy

Surgery to remove the breast, chest muscles, and the lymph nodes of the armpit. For many years, this was the operation most used, but it is now used only when the cancer has spread to the chest muscles.


Capable of emitting high-energy rays or particles.


A doctor with special training in the use of x-rays (and related technologies such as ultrasound, MRI and radioactive tracers) to diagnose and investigate disease.


Refers to cancer cells that are not sensitive to radiation. In these cases, radiation therapy will not likely achieve the desired result. Cells that divide slowly tend to be radioresistant.


Refers to the susceptibility of cells, cancerous or healthy, to respond to radiation therapy. Cells that divide rapidly are especially radiosensitive and more likely to respond to radiation.


Drugs that make cells more sensitive to radiation.


When people elect to be a part of a clinical trial, the treatment they receive may be chosen by randomization. Randomization is the process of using chance (like the flip of a coin) to assign a person to either the treatment group or control group of the trial. Randomization is a method used to prevent bias in research.

Randomized clinical trial

A study in which patients with similar traits, such as type of cancer and extent of disease, are assigned by chance (like the flip of a coin) to either the treatment group or the control group for the purpose of comparing different treatments. Because the patients are assigned to the groups randomly (not by irrelevant factors such as preferences) the both the study groups can be considered comparable and the results of the different treatments can be compared. The researcher does not know in advance which treatment might be better. It is a patient’s choice to enter a randomized clinical trial. (see also clinical trials).

Reconstructive surgery

Surgical procedure done to restore the shape or function of an area of the body altered by cancer surgery.

Rectal Cancer Cancer that occurs in the last 6-8 inches of the large intestine. Rectal cancer may be treated with chemotherapy and/or radiation therapy prior to surgery.


The last 6-8 inches of the large intestine. The rectum stores solid waste until it leaves the body through the anus.

Recur, recurrence

The return of cancer, at the same site as the original (primary) tumor or in another location after it had been in remission or disappeared for a period of time.

Recurrent Breast Cancer Recurrent disease means that the cancer has come back (recurred) after it has been treated. It may come back in the breast, in the soft tissues of the chest (the chest wall), or in another part of the body.

Red blood cells (RBC)

Also called erythrocytes. These are the cells that carry oxygen throughout the body. They are also the cells that make blood red. RBC is part of the complete blood count (CBC). The normal range for RBC is 4.5-6.0 M/uL (male) and 4.2-5.4 M/uL (female), although ranges may vary in different laboratories.

Reed-Sternberg cell

The type of abnormal cell present in Hodgkin’s lymphoma. These cells are named for the pathologists who discovered them.


The state of growing smaller or disappearing; used to describe the shrinkage or disappearance of a cancer.


The return of disease or symptoms after an apparent recovery or remission.

Relaxation techniques

Methods used to reduce tension, stress and anxiety as well as manage pain. Relaxation techniques may include listening to music, tightening and relaxing muscle groups, deep breathing, yoga, and others.


Disappearance of the signs and symptoms of cancer. When this happens, the disease is said to be "in remission." A remission can be temporary or permanent.

Renal Cell Cancer (Renal Cell Carcinoma)

Cancer that develops in the lining of the renal tubules, which filter the blood and produce urine. Renal cell cancer represents 3% of all cancers.

Renal pelvis

Area at the center of the kidney where urine collects and is funneled into the ureter.

Reproductive system

The organs that are directly involved in producing children. These include the testicles, penis, vagina, ovaries and uterus.

Residual disease

Disease that may be remaining after therapy.

Retinoblastoma A malignant (cancerous) tumor of the retina. The retina is the thin nerve tissue that lines the back of the eye that senses light and forms images. Retinoblastoma is thought to be caused by the loss of tumor-suppressor genes; the inherited form typically appears in childhood, since one gene is missing from the time of birth.
Rhabdomyosarcoma A type of soft tissue sarcoma which arises in the skeletal muscle areas that can be controlled voluntarily, such as the eye, bladder, arms and legs. This is the most common soft tissue sarcoma in children aged 1 to 3 years, accounting for slightly more than half of all soft tissue sarcomas. Soft tissue sarcomas are uncommon malignant tumors that begin in the soft tissues such as muscles, cartilage, fat, or connective tissue. Each year, in the United States, there are about 6,000 cases of soft tissue sarcomas, making up 1% of all cancers in adults and 15% of all cancers in children. There are at least 56 different types of soft tissue sarcomas named according to the normal tissues from which the tumor is derived. In most cases, surgery is considered first-line therapy.


A measure of the likelihood of some uncertain or random event with negative consequences for human life or death.

Risk factor

A habit, trait, or condition that increases the chance of developing a disease.

Risk/benefit ratio

The relation between the risks and benefits of a given treatment or procedure. Institutional Review Boards (IRBs), located where the study is to take place, determine that the risks in a study are reasonable with respect to the potential benefits. It is also up to the patient to decide if it is reasonable for to take part in the study.


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