Clinical Trial / Cancer Definitions


The number of patients entered into a study. Each clinical trial requires a specific number of participants in order to provide adequate information for analysis to answer the specific questions asked in the study.


A National Cancer Institute (NCI)-funded cancer cooperative group. ACOSOG stands for American College of Surgeons Oncology Group.


A National Cancer Institute (NCI)-funded cancer cooperative group). ACRIN stands for American College of Radiology Imaging.

Action Study

In cancer prevention clinical trials, a study that focuses on finding out whether actions people take can prevent cancer.

Adjunctive Therapy

Another treatment used together with the primary treatment. Its purpose is to assist the primary treatment.

Adjuvant Therapy

Treatment given after the primary treatment to increase the chances of a cure. Adjuvant therapy may include chemotherapy, radiation therapy, hormone therapy, or biological therapy.

Adverse Effect

An unwanted side effect of treatment.

Agent Study

In cancer prevention clinical trials, a study that tests whether taking certain medicines, vitamins, minerals, or food supplements can prevent cancer. Also called chemoprevention study.

AJCC Staging System

A system developed by the American Joint Committee on Cancer for describing the extent of cancer in a patient’s body. The descriptions include TNM: T describes the size of the tumor and if it has invaded nearby tissue, N describes any lymph nodes that are involved, and M describes metastasis (spread of cancer from one body part to another).


A process in which anything complex is separated into simple or less complex parts. In clinical trials, analysis typically refers to the review and interpretation of data collected during the study.

Anecdotal Report

An incomplete description of the medical and treatment history of one or more patients. Anecdotal reports may be published in places other than peer-reviewed, scientific journals.

Animal Model

An animal with a disease either the same as or like a disease in humans. Animal models are used to study the development and progression of diseases and to test new treatments before they are given to humans. Animals with transplanted human cancers or other tissues are called xenograft models.


Prevention of the growth of new blood vessels.


A specific therapy program under study, often used interchangeably with treatment program, treatment regimen, treatment arm, or treatment. Used when referring to a particular treatment regimen in a study that has more than one regimen.

Antibody Therapy

Treatment with an antibody, a substance that can directly kill specific tumor cells or stimulate the immune system to kill tumor cells.

Antihormone Therapy

Treatment with drugs, surgery, or radiation in order to block the production or action of a hormone. Antihormone therapy may be used in cancer treatment because certain hormones are able to stimulate the growth of some types of tumors.


A substance that blocks the formation of neoplasms (growths that may become cancerous).