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Oncology Glossary

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lactate dehydrogenase (LDH): an enzyme found in the blood and other body tissues and involved in energy production in cells. High levels of lactate dehydrogenase in the blood may indicate tissue damage, cancer, or another disease.

LAGE-1: member of the NY-ESO-1 gene family. LAGE-1 is also called CTAG2.

lamins: members of the intermediate filament family of proteins. Lamins are helical filament-shaped proteins that provide structural support for the nuclear envelope through a meshwork of filaments attached to the inner layer of the nuclear membrane. Lamins are categorized into A-type (expressed in differentiated somatic cells) and B-type (expressed in all cells) subfamilies.

landmark analysis: the conditional landmark analysis selects a fixed time during follow-up as the landmark. The subset of patients still in the study at the landmark time is separated into categories described by the classifying event and observed forward in time. Patients who cease follow-up before the landmark time are excluded from the analysis, and membership in the classifying event group is defined at the landmark time regardless of any shifts that may occur later. In essence, the analysis clock is reset at the landmark.

lapatinib: a dual tyrosine kinase inhibitor. Lapatinib has been developed as an inhibitor of the tyrosine kinase activities of ErbB1 (EGFR) and ErbB2. Like other tyrosine kinase inhibitors, it competes with ATP binding to the intracellular regions of the receptors that are activated after tyrosine phosphorylation.

laser-capture microdissection (LCM): a method for isolating pure cells of interest from specific microscopic regions of tissue sections.

(LC)-LC-MS/MS: two-dimensional liquid chromatography coupled to tandem mass spectrometry.

LCK: a lymphocyte-specific protein tyrosine kinase belonging to the Src family of nonreceptor protein tyrosine kinases. LCK is primarily expressed on T cells and some B cells and is involved in the development of immature thymocytes.

leave-one-out cross validation: validation in which test sets of one sample are chosen and the accuracy of the model derived from the remaining (n – 1) samples is scored. This is repeated for all the “n” samples so that every sample acts as a test set. The predictive error obtained can be used as a measure of internal validation of the predictive power of the classifier developed using the full data set. All aspects of the classifier development process should be repeated from scratch for each leave-one-out training set, including all aspects of gene selection or tuning parameter optimization.

leiomyosarcoma: a cancer of the smooth muscle (or its precursors). Common primary sites for this tumor include the uterus, small intestine or stomach, or the wall of a blood vessel in the abdomen, in the extremity, or in the skin.

lentiginous growth pattern: an intraepidermal growth pattern in which melanocytes are arranged predominantly as single units within the basal layer of the epidermis.

less than pathologic complete response: the presence of any residual tumor cells in a histologic evaluation of a tumor specimen.

letrozole: a noncorticosteroidal inhibitor of the enzyme aromatase, which is important in the conversion of androgen to estrogen in the peripheral tissues of postmenopausal women. Because hormone-dependent breast cancer progresses with estrogen, letrozole has been used in the treatment of breast cancer in postmenopausal women. See aromatase inhibitors.

leukotrienes: biologically active products of arachidonic acid metabolism and formed by the action of the enzyme 5-lipoxygenase. Leukotrienes play a major role in the inflammatory response to injury and have been implicated in the pathogenesis of several inflammatory diseases, including asthma, rheumatoid arthritis, inflammatory bowel disease, and cancer. Their role as inflammatory mediators of disease has made them attractive for therapeutic targets.

Lewis lung carcinoma model: a primary murine lung carcinoma propagated in C57BL/6 mice.

life expectancy: the average number of years that an individual would live if he or she were to experience throughout life the age-specific mortality rates prevailing in a given year.

life table: a table for a given population listing for each sex and each age how many members die at that age and how many survive 1 more year of life.

linear regression analysis: the estimation of the slopes for each of the explanatory variables in a linear regression model. That is, finding the best fit line.

linear regression model: a mathematical equation in which a continuous outcome variable is a linear combination of one or more explanatory variables, plus random noise.

linkage disequilibrium: nonrandom association of linked genes. This is the tendency of the alleles of two separate but already linked loci to be found together more frequently than would be expected by chance alone.

lipoxygenases: enzymes that are involved in the synthesis of leukotrienes, key mediators of inflammation.

LIV1: gene encoding LIV-1, a protein belonging to the subfamily of zinc transporters. An estrogen-regulated gene, LIV1 has been implicated in the metastatic spread of estrogen-positive breast cancer to the lymph nodes.

LMP1 (latent membrane protein 1): Epstein-Barr virus (EBV) –expressed protein expressed in latent phases II and III of EBV infection. LMP1 is an activation protein that is responsible for the activation of several cellular pathways (eg, JAK-STAT, NF-κB, JNK, SAPK) that are normally not activated in quiescence cells.

LMP2: Epstein-Barr virus (EBV) -expressed protein expressed in latent phases II and III of EBV infection. The protein interacts with B-cell receptor tyrosine kinase and regulates its activity negatively. It prevents the activation of the lytic cycle after EBV infection.

locked nucleic acid: is a modified RNA nucleotide, often referred to as inaccessible RNA. The ribose moiety of an LNA nucleotide is modified with an extra bridge connecting the two oxygen and four carbon. The bridge locks the ribose in the 3-endo (north) conformation, which is often found in the A-form of DNA or RNA. LNA nucleotides can be mixed with DNA or RNA bases in the oligonucleotide. The locked ribose conformation enhances base stacking and backbone preorganization. This significantly increases the thermal stability (melting temperature) of oligonucleotides.

locoregional failure: failure at the primary site or the regional lymphatics.

locoregional progression-free survival: the time to tumor progression within the volume treated by radiation (typically covering the primary site and adjacent lymph node areas) or time to death.

logistic regression analysis: a multivariable regression model in which the log of the odds of a time-fixed outcome event (eg, 30-day mortality) or other binary outcome is related to a linear equation.

logistic regression model: a multivariable prediction model in which the log of the odds of a time-fixed outcome event or other binary outcome is related to a linear equation.

lonafarnib: a farnesyl transferase inhibitor. See FT (farnesyltransferase).

loss of heterozygosity (LOH): a situation in which one chromosome has a normal allele of a gene and one chromosome has a mutant or deleted allele.

LTB4 (leukotriene B4): secreted by myeloid and nonmyeloid cells from arachidonic acid through the action of several enzymes, including 5-lipoxygenase. Leukotriene B4 modulates immune responses and mediates inflammatory reactions, including those involved in chemotaxis, chemokinesis, and vasoactive responses. It is also important in neutrophil and endothelial cell adhesion.

LTB4 receptor: one of the G-coupled receptors, which are members of the rhodopsin-like receptor superfamily and present on human leukocytes. The LTB4 receptor on the surface of neutrophils has high and low affinity binding sites for LTB4. Binding of LTB4 to the receptor induces neutrophil chemotaxis.

luminal epithelial tumors: human breast tumors that are characterized by the expression of genes typically expressed in the cells that line the ducts of normal mammary glands. These genes include the estrogen receptor, GATA3, X-box binding protein 1, FOXA1, and cytokeratins 8 and 18.

LY293111: a diaryl carboxylic acid derivative. LY293111 is a selective leukotriene B4 receptor antagonist. By inhibiting the production of leukotriene B4, LY293111 is an antagonist of the proinflammatory actions of leukotriene B4, which includes neutrophil chemotaxis, aggregation, and calcium mobilization.

lymph node ratio: the ratio between the number of involved to the number of resected nodes.

lymphangiogenesis: formation of the lymphatic network of capillaries. Unlike capillaries of the blood vascular system, lymphatic capillaries are characterized by a lining of a single layer of endothelial cells, devoid of fenestrations, with poorly developed junctions and the presence of frequent, large interendothelial gaps. Additionally, lymphatic capillaries lack a continuous basement membrane and are devoid of pericytes. Although lymphangiogenesis has an important physiological role in homeostasis, metabolism, and immunity, it has also been implicated in diseases such as neoplasm metastasis, edema, rheumatoid arthritis, psoriasis, and impaired wound healing. Podoplanin, LYVE-1 (lymphatic vessel endothelial hyaluronan receptor 1), PROX-1, desmoplakin, and the vascular endothelial growth factor (VEGF) -C/VEGF-D receptor VEGF receptor-3 are important markers specific to lymphangiogenesis.

lymphatic metastases: tumor spread via lymphatics affecting lymph nodes. Lymphatic metastases are linked to lymphatic dissemination of tumors, which occurs either via intratumoral lymphatics or as a result of an increase in surface area of lymphatics at tumor margins. Vascular endothelial growth factor (VEGF) -C and VEGF-D are growth factors linked to lymphatic dissemination of tumors and, consequently, along with VEGF receptor-3 are important predictors of poor survival.

lymphovascular invasion (LVI): the presence of lymphatic or vascular vessels invading a tumor. The presence of lymphovascular invasion in primary breast tumors increases the risk of metastasis to the regional lymph node and systemic organ sites and is therefore considered a poor prognostic factor.

Lynch syndrome: hereditary nonpolyposis colorectal cancer (HNPCC). A cancer syndrome characterized by Henry T. Lynch in 1966, this genetic condition has a high risk of colon cancer as well as other cancers including endometrial, ovary, stomach, small intestine, hepatobiliary tract, upper urinary tract, brain, and skin.

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