B

Bacterial artificial chromosome (BAC): A vector used to clone DNA fragments (100- to 300-kb insert size; average, 150 kb) in Escherichia coli cells. Based on naturally occurring F-factor plasmid found in the bacterium E. coli. Compare cloning vector

Bacteriophage: (See: Phage.)

Barium enema with air contrast: (See: Double contrast barium enema.)

Basal cell carcinoma : Most common non-melanoma skin cancer. It begins in the lowest layer of the epidermis, called the basal cell layer. It usually develops on sun-exposed areas, especially the head and neck. Basal cell cancer is slow-growing and is not likely to spread to distant parts of the body. 

Base pair (bp): Two nitrogenous bases (adenine and thymine or guanine and cytosine) held together by weak bonds. Two strands of DNA are held together in the shape of a double helix by the bonds between base pairs.

Base sequence: The order of nucleotide bases in a DNA molecule.

Base sequence analysis: A method, sometimes automated, for determining the base sequence.

Basic science: Lab studies not aimed at specific problems, but that provide necessary knowledge and background for later applied research. 

B-cells : White blood cells involved in making antibodies. 

Behavioral research : Study of what motivates people to act as they do. The results of such research is used to help convince people to adopt healthy lifestyles. 

Benign : Not cancerous. 

Benign prostatic hyperplasia (BPH) : Non-cancerous enlargement of the prostate that may cause problems with urination such as trouble starting and stopping the flow. 

Benign tumor : Non-cancerous abnormal growth that does not spread to other parts of the body. 

Beta-carotene : Early form of vitamin A found mainly in yellow and orange vegetables and fruits. It functions as an antioxident and may play a role in cancer prevention. 

Bilateral : On both sides of the body.

Biotechnology: A set of biological techniques developed through basic research and now applied to research and product development. In particular, the use by industry of recombinant DNA, cell fusion, and new bioprocessing techniques.

Biologic response modifiers (BRM) : Substances that boost the body's immune system to fight cancer. Interferon is one such BRM, ( Also called " biologic therapy".) 

Biomarkers : ( See: Tumor markers.)

Biopsy : Removal of tissue to see whether cancer cells are present. There are several kinds of biopsies. In some, a very tiny needle is used to draw fluid and cells from a lump. In a core biopsy, a larger needle is used to remove more tissue.

BIvalent: Having a combining power of two atoms of hydrogen.  In cytology, a structure consisting of two paired homologous chromosomes, each split into two "sister" chromatids during meiosis.

Blood count : A count of the number of red and white blood cells in a given sample of blood. 

B-lymphocytes or B-cells: White blood cells involved in making antibodies. 

Bone marrow : Soft tissue in the hollow of bones that produces new blood cells. 

Bone marrow aspiration and biopsy : Procedure wherein a needle is inserted into the cavity of a bone, usually the hip or breast bone, to remove a small amount of bone marrow for examination under a microscope. 

Bone marrow transplant : Complex but common treatment used when cancer is advanced or has recurred, or as the main treatment in some types of leukemia. Bone marrow transplantation makes possible the use of very high dose chemotherapy, which would otherwise be impossible. " Autologous bone marrow transplant" means that the patient's own bone marrow is used. An " allogeneic bone marrow transplant" uses marrow from a donor whose tissue type closely matches the patient's. Leukemia patients usually have allogenic transplants. Basically, a portion of the patient's ( or donor's) bone marrow is withdrawn, cleaned, treated, and stored. Then the patient is given high doses of chemotherapy to kill cancer cells. These drugs also destroy the patient's remaining bone marrow, robbing the body of its ability to fight infection. The cleansed and stored marrow is given by transfusion (transplanted) to restore the immune system. It is a risky procedure that involves a lengthy and expensive hospital stay that may not be covered by health insurance. The best place to have a bone marrow transplant is at a comprehensive cancer center or other facility that has the technical skill and experience to perform it safely.

Bone scan : Imaging method that gives important information about bones, including location of cancers that may have spread to the bones. Scans can be done on an outpatient basis and are painless, except for the needle stick used to deliver low-dose radioactive substance through a vein. Pictures shows where radioactivity collects, pointing to an abnormality. 

Bone survey : X-ray of the entire skeleton; often done when looking for metastasis to the bones. 

BP: (See: base pair.)

BPH: (See benign prostatic hyperplasia.)

Brachytherapy : Placement of radioactive material directly into a tumor or close to it. ( Also called interstitial radiation therapy or seed implantation.) 

Brain scan : Imaging method used to find ab normalities in the brain, including brain cancer and cancer that has spread to the brain from other places in the body. Brain scans can be done in outpatient clinics. Scans painless, except for the needle stick when a radioactive substance is injected into a vein. Scan pictures show where radioactivity collects, indicating an abnormality. 

BRCA1: Gene which, when damaged or mutated, places a woman at greater risk for breast and/or ovarian cancer, compared with women who do not have the mutation. In a woman with a BRCA1 mutation, the estimated lifetime risk of breast cancer is about 50% compared with 12% in the general population. A person who has this mutated gene has a 50% chance of passing on the gene to her children. There is a genetic test for the gene, but it is recommended only for women who are known to be at risk because several women in their family have had breast or ovarian cancer before menopause.

BRCA2 : Gene that, when damaged or mutated, puts a woman at much higher risk for breast cancer and/or ovarian cancer than the general population. In a woman with a BRCA2 mutation, the estimated lifetime risk of breast cancer is 50% to 60%. BRCA2 and BRCA1 together account for about 80% of the breast cancer that occurs in women with strong family histories of the disease. BRCA2 is also thought to raise the risk for breast cancer in men. There is a genetic test for BRCA2 but it is only recommended for those with strong family histories of breast or ovarian cancer.

Breast cancer : Main types - ductal carcinoma in situ, invasive ductal carcinoma, lobular carcinoma in situ, invasive lobular carcinoma, medullary carcinoma, and Paget's disease of the nipple (see definitions under each of these headings). Some breast specialists believe that lobular carcinoma in situ is not a true cancer. 

Breast conservation therapy : Surgical removal of a breast cancer and a small area of normal tissue surrounding the cancer without removing any other part of the breast. The lymph nodes under the arm may be removed, and radiation therapy often also is given after surgery. Also called lumpectomy, segmental excision, limited breast surgery, or tylectomy. 

Breast implant : Sac used to increase breast size or restore contour after mastectomy. The sac is filled with silicone gel or sterile saltwater (saline).

Breast reconstruction : Surgery that rebuilds breast contour after mastectomy. A breast implant or the woman's own tissue is used. The nipple and areola also can be re-created. Reconstruction can be done at the time of mastectomy or any time later. 

Breast self-exam (BSE) : Checking breasts for lumps or suspicious changes. BSE is recommended for all women over age 20, once a month, usually at a time other than days before, during, or immediately after menstrual period. 

Bronchi : The two main air passages in the lungs that lead to the windpipe (trachea). Bronchi provide a passage for air to move in and out of the lungs. 

Bronchiole : One of the smaller sub-divisions of the bronchi. 

Bronchoscopy : Exam of the bronchi using a flexible, lighted tube (bronchoscope).