| tumor | 1. <oncology> An abnormal mass of tissue that results from excessive cell division that is uncontrolled and progressive, also called a neoplasm. Tumours perform no useful body function. They may be either benign (not cancerous) or malignant. 2. Swelling, one of the cardinal signs of inflammations, morbid enlargement. Origin: L. Tumere = to swell (12 May 1997) |
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| tumor marker | <investigation, oncology> A substance in the body that usually indicates the presence of cancer. These markers are usually specific to certain types of cancer and are usually found in the blood or other tissue samples. Examples are alphafetoprotein (AFP), human chorionic gonadotropin, and lactate dehydrogenase (LDH). They may be indicators of tumour stage and grade as well as useful for monitoring responses to treatment and predicting recurrence. Many chemical groups are represented including hormones, antigens, amino and nucleic acids, enzymes, polyamines, and specific cell membrane proteins and lipids. (18 Jul 2002) |
| tumor necrosis factor | <cytokine> Originally described as a tumour inhibiting factor in the blood of animals exposed to bacterial lipopolysaccharide or Bacille Calmette-Guerin. Preferentially kills tumour cells in vivo and in vitro, causes necrosis of certain transplanted tumours in mice and inhibits experimental metastases. Human Tumour Necrosis factor alpha is a protein of 157 amino acids and has a wide range of pro inflammatory actions. Usually considered a cytokine. Synonym: cachectin. Acronym: TNF (13 Nov 1997) |
| collision | <physics> Refers to the close approach of two or more particles, photons, atoms, nuclei, etc, during which such quantities as energy, momentum, and charge may be altered. More-or-less synonymous with scattering, except in scattering one generally thinks of one of the particles as being at rest, and the other colliding particles scatter from their initial direction of motion due to the collision. (09 Oct 1997) |
| collision cross-section | <radiobiology> Effective surface area of a particle when it collides with another, describes probability of collisions between the two particles. (09 Oct 1997) |
| collision frequency | <chemistry> The rate at which chemical species collide, used in theories of chemical kinetics. Also, the frequency with which gaseous molecules collide. (09 Oct 1997) |
| collision theory | <chemistry> A mathematical description of the number of collisions between molecules in a sample of matter per unit time, useful for predicting rates of reaction. (09 Oct 1997) |
| collision time | <radiobiology> Typical time which passes between two consecutive collision events for a given particle. Inverse of the collision frequency, equal to the mean free path divided by the particle's velocity. In plasmas, the (Coulomb) collision time decreases with increasing density, and increases with increasing temperature. (09 Oct 1997) |
| collision tumour | Two originally separate tumour's, especially a carcinoma and a sarcoma, that appear to have developed by chance in close proximity, so that an area of mingling exists. See: carcinosarcoma. (05 Mar 2000) |
| coulomb collision | <physics> An interparticle collision where the Coulomb's force (electrical attraction and repulsion) is the governing force. Coulomb collisions have a number of interesting properties, but these are better described in textbooks. The interaction of the charged particles with each other's electric fields results in deflections of the particles away from their initial paths. See: Coulomb's Law, electrostatic force. (21 Jun 2000) |
| effective collision radius | <radiobiology> Effective size of a particle equal to the square root of (cross-section/pi). Determines the effective range of interaction of the particle. (09 Oct 1997) |