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·         labeling index   A measure of the fraction of dividing cells that are detected by a immunohistochemical stain of the tumor cells.

·         LAK cells   Lymphokine activated killer cells are transformed in the laboratory from lymphocytes. They attack tumor cells. LAKs are “super charged” natural killer cells created by exposing natural killer (NK) cells to IL-2 (interleukin 2).

·         laser   [lay´ zur]   Light Amplification by Stimulated Emission of Radiation. A tool used in addition to or in place of a scalpel. It creates intense heat and power when focused at close range, destroying cells by vaporizing them. Lasers are frequently used with stereotactic localization to direct their beams. They are used in microsurgery, photodynamic therapy and for a variety of diagnostic purposes.

·         laser-capture microdissection   A sophisticated technique for examining tumor tissue. It allows specific cells to be removed from a sample of tissue for detailed study. Abbreviated LCM.

·         lateral   On the side, as the lateral ventricles are located on both the right and left sides of the brain.

·         lateral ventricles   [ven´ tri kls]   The two fluid-filled cavities located in the cerebral hemispheres.

·         LCSW   Licensed Clinical Social Worker.

·         LENT   Late effects on normal tissue. Long-term side-effects of treatment, especially radiation therapy.

·         leptomeningeal cancer   Cancer cells in cerebrospinal fluid which flows throughout the subarachnoid space, the area between the pia mater and arachnoid layers of the meninges. Also called leptomeningeal metastasis.

·         leptomeningeal cyst   [lep´ toe meh nin jee´ al • sist] An enlarged, fluid-filled area of the subarachnoid space — the space between the arachnoid and pia mater layers of the meninges. Can occur in both adults and children. Also called an arachnoid cyst.

·         leptomeninges   The arachnoid and pia mater layers of the meninges.

·         lesion   [lee´ zhun]   An area of abnormal tissue due to disease or injury.

·         lethargy   [leth´ ar gee]   Sluggishness, drowsiness, indifference.

·         leukocytes   [lou´ ko sitez]   White blood cells, including eosinophils, basophils, mast cells, neutrophils, lymphocytes and monocytes, etc.

·         leukoencephalopathy   [loo koe n seff ah lopp´ ah thee]   Injury to the white matter of the brain. Can be due to infection, drugs, radiation, or disease. Symptoms range from mild to severe.

·         Li-Fraumeni syndrome   A rare, inherited predisposition to multiple cancers including brain tumors. It is caused by an alteration in the p53 suppressor gene. Abbreviated LFS.

·         limbic system   The part of the brain involved with behavior, emotion, and the sense of smell. With the hypothalamus, it controls hunger, thirst, and biological rhythms.

·         Linac Radiosurgery   An adapted linear accelerator that delivers a single, high-energy beam, computer-shaped to the tumor.

·         linear accelerator   An electrical device that creates ionizing radiation in the form of x-rays (photons) The higher the voltage of the device, the more penetrating are the x-rays produced.

·         lipoma   A rare, benign tumor composed of fat tissue.

·         lobe   One of four sections of the cerebral hemispheres.

·         lobectomy   [low bek´ toe mee]   The surgical removal of one lobe of the brain.

·         local   In the area of the tumor; confined to one specific area. Also referred to as localized.

·         local therapy   A treatment directed only to the tumor and perhaps a small area beyond it.

·         loss of 1p 19q  The combined loss of genetic material on chromosomes 1p and 19q is strongly associated with favorable outcome in patients with certain types of oligodendroglial tumors (oligodendrogliomas).

·         low-frequency electromagnetic fields   Low energy fields, called EMFs, emitted by power lines and household appliances.

·         lower toxicity drugs   A generation of chemotherapy drugs with milder side-effects.

·         LPN   Licensed Practical Nurse.

·         LRRFS   Local/Regional Recurrence-Free Survival.

·         LSW   Licensed Social Worker.

·         lumbar   [lum´ bar]   The area of the spine between the ribs and the pelvis (the waist and lower back).

·         lumbar puncture   Needle penetration into the subarachnoid space of the lumbar spine. Used to withdraw a sample of spinal fluid for examination or to to inject a dye into the spine prior to a myelogram. Also called spinal tap.

·         lymph   [limf]   A transparent, slightly yellow fluid that carries lymphocytes, bathes body tissues and drains into the lymphatic vessels.

·         lymph nodes   [limf]   Small bean-shaped organs of the immune system, distributed widely throughout the body and linked by lymphatic vessels. Clusters of lymph nodes are found in the underarms (axilla), groin, neck, chest and abdomen. Also called lymph glands, although they are not actually glands.

·         lymphatic system   [lim fat´ ik]   The tissues and organs that produce, store and carry white blood cells that fight infections and other diseases.

·         lymphatic vessels   [lim fat´ ik]   A bodywide network of channels, similar to the blood vessels, which transport lymph fluid to the immune organs and into the bloodstream.

·         lymphocyte   [lim´ foe site]   A lymph cell, the main type of immune cell. They are one type of white blood cell and are formed in the lymph system. Lymphocytes produce antibodies and interferons.

·         lymphokine activated killer cells   Cells transformed in the laboratory from lymphocytes. They attack tumor cells. Lymphokine activated killer cells are “super charged” natural killer cells created by exposing natural killer (NK) cells to IL-2 (interleukin 2). Abbreviated LAK cells.

·         lymphokines   [lim´ foe kinez]   Powerful chemical substances that help direct and regulate immune responses. Lymphokines are biological response modifiers.

·         lymphoma   [lim foe´ ma]   Cancer that arises from cells of the lymphatic system. In the brain, this type of cancer is called Primary CNS Lymphoma (PCL).