I

Ileostomy: Operation in which the end of the small intestine (ileum) is brought out through an opening in the abdomen. The contents of the intestine, unformed stool, are expelled through this opening into a bag called an "appliance".

Imaging studies: Production of pictures of internal body structures. Some imaging methods used to detect cancer are x-rays, CT scans, magnetic resonance imaging (MRI), and ultrasound.

Immune system: System that resists infection by microbes such as bacteria or viruses and rejects transplanted tissues or organs. The immune system may also help the body fight some cancers.

Immunology: Study of how the body resists infection and some diseases.

Immunosuppression: State in which the ability of the body's immune system to respond is decreased. Some individuals are born with this condition. It also may be caused by certain infections (such as human immunodeficiency virus or HIV), or by certain cancer therapies, such as cancer-cell killing (cytotoxic) drugs, radiation, and bone marrow transplants. 

Immunotherapy: Treatment that promotes or supports the immune system response to cancer and other diseases.

Implant: Tiny amount of radioactive material placed in or near a cancer. Also, an artificial form used to restore the shape of an organ after surgery, for example, a breast implant.

Impotence, Impotent: Not able to have or keep an erection of the penis. 
Incidence: Number of new cases of a disease occuring in a population each year.

Incontinence: Complete or partial loss of urinary control.

Infiltrating ductal carcinoma: Cancer starting in the milk passages (ducts) of the breast and then breaking through the duct wall, where it invades the fatty tissue of the breast. When it reaches this point, it has the potential to spread (metastasize) elsewhere in the breast, as well as to other parts of the body through the bloodstream and lymphatic system. Infiltrating ductal carcinoma is the most common type of breast cancer, accounting for about 80% of breast malignancies. Also known as invasive ductal carcinoma.

Infiltrating lobular carcinoma: Cancer starting in milk-producing glands (lobules) of the breast that then breaks through the lobule walls to involve the nearby fatty tissue. From there, it may spread elsewhere in the breast. About 15% of invasive breast cancers are invasive lobular carcinomas. It is often hard to detect by physical examination or even by mammography. Also called invasive lobular carcinoma.

Inflammatory bowel disease: Chronic inflammatory bowel disease (ulcerative colitis or Crohn's disease) is a condition in which the colon is inflamed over a long period of time and may have ulcers in its lining.
Informatics: The study of the application of computer and statistical techniques to the management of information. In genome projects, informatics includes the development of methods to search databases quickly, to analyze DNA sequence information, and to predict protein sequence and structure from DNA sequence data.

Informed consent: Legal document by which patients agree to treatment. It explains the course of treatment, risks, benefits, and possible alternatives.

Infraclavicular nodes: Lymph nodes located beneath the collar bone (clavicle).

In situ: Localized and confined to one area only. A very early stage of cancer that is usually the most successfully treatable.

In situ hybridization: Use of a DNA or RNA probe to detect the presence of the complementary DNA sequence in cloned bacterial or cultured eukaryotic cells.

Interferon: A protein produced by cells that helps regulate the immune system, boosting activity when a threat, such as a virus, is found. Interferon helps fight some types of cancer.

Intraductal carcinoma: (See: Ductal carcinoma)

Interleukins: (See: Cytokine.)

Interphase: Period in cell cycle when DNA is replicated in the nucleus; followed by mitosis.
Interstitial radiation therapy: Placement of radioactive implants directly into tissue (not a body cavity).

Intravenous pyelogram: Type of x-ray procedure in which dye is injected into the bloodstream. It travels to the kidneys, ureters and bladder and helps to clearly outline these organs on the x-rays. Referred to as IVP.
Intron: The DNA base sequence interrupting the protein coding sequence of a gene; this sequence is transcribed into RNA but is cut out of the message before it is translated into protein. (Compare: Exon.)

Invasive cancer: One that has spread beyond the layer of cells where it first developed to involve adjacent tissue.

Invasive ductal carcinoma: Cancer starting in the milk passages (ducts) of the breast and then breaking through the duct wall, where it invades the fatty tissue of the breast. When it reaches this point, it has the potential to spread (metastasize) elsewhere in the breast, as well as to other parts of the body through the bloodstream and lymphatic system. Invasive ductal carcinoma is the most common type of breast cancer, accounting for about 80% of breast malignancies. Also known as infiltrating ductal carcinoma.

Invasive lobular carcinoma: Cancer starting in milk-producing glands (lobules) of the breast that then breaks through the lobule walls to involve the nearby fatty tissue. From there, it may spread elsewhere in the breast. About 15% of invasive breast cancers are invasive lobular carcinomas. It is often hard to detect by physical examination or even by mammography. Also called infiltrating lobular carcinoma.

IVP : (See: Intravenous pyelogram.

In vitro: Outside a living body or organism.

In vivo: Inside a living body or organism.