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tissue composed of cells that grow in an abnormal way. Normal tissue is growth-limited, i.e., cell reproduction is equal to cell death. Feedback controls limit cell division after a certain number of cells have developed, allowing for tissue repair but not expansion. Tumor cells are less responsive to these restraints and can proliferate to the point where they disrupt tissue architecture, distort the flow of nutrients, and otherwise do damage.

Tumors may be benign or malignant. Benign tumors remain localized as a discrete mass. They may differ appreciably from normal tissue in structure and excessive growth of cells, but are rarely fatal. However, even benign tumors may grow large enough to interfere with normal function. Some benign uterine tumors, which can weigh as much as 50 lb (22.7 kg), displace adjacent organs, causing digestive and reproductive disorders. Benign tumors are usually treated by complete surgical removal. Cells of malignant tumors, i.e., cancerscancer,
in medicine, common term for neoplasms, or tumors, that are malignant. Like benign tumors, malignant tumors do not respond to body mechanisms that limit cell growth.
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, have characteristics that differ from normal cells in other ways beside cell proliferation. For example, they may be deficient in some specialized functions of the tissues where they originate. Malignant cells are invasive, i.e., they infiltrate surrounding normal tissue; later, malignant cells metastasize, i.e., spread via blood and the lymph system to other sites.

Both benign and malignant tumors are classified according to the type of tissue in which they are found. For example, fibromas are neoplasms of fibrous connective tissue, and melanomas are abnormal growths of pigment (melanin) cells. Malignant tumors originating from epithelial tissue, e.g., in skin, bronchi, and stomach, are termed carcinomas. Malignancies of epithelial glandular tissue such as are found in the breast, prostate, and colon, are known as adenocarcinomas. Malignant growths of connective tissue, e.g., muscle, cartilage, lymph tissue, and bone, are called sarcomas. Lymphomas and leukemiasleukemia
, cancerous disorder of the blood-forming tissues (bone marrow, lymphatics, liver, spleen) characterized by excessive production of immature or mature leukocytes (white blood cells; see blood) and consequently a crowding-out of red blood cells and platelets.
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 are malignancies arising among the white blood cells. A system has been devised to classify malignant tissue according to the degree of malignancy, from grade 1, barely malignant, to grade 4, highly malignant. In practice it is not always possible to determine the degree of malignancy, and it may be difficult even to determine whether particular tumor tissue is benign or malignant.


An aberrant new growth of abnormal cells or tissues; a tumor.
References in periodicals archive ?
Furthermore, the neoplastic cells failed to react with histochemical stain, although the colloidal substances appeared pale.
In what they called "the first methodological[ly] sound prospective study which shows that PPIs strongly reduce the risk of neoplastic progression in BE," Dr.
MRI remains the mainstay for differentiating between neoplastic and non-neoplastic lesions.
Also standard myocardial revascularization with Cardiopulmonary Bypass (CPB) and aortic cross clamping has potential deleterious effects on neoplastic patients, enhancing the systemic inflammatory response and attenuating the immune response (3,4).
Cases of disseminated neoplasia in bivalve mollusc species are characterized by the presence of large (2-4 times the diameter of normal hemocytes), neoplastic circulating cells that have a hyperchromatic and often pleomorphic nucleus containing 1 or more prominent nucleoli (Barber 2004), and a high nuclear-tocytoplasmic volume ratio in neoplastic cells (Mix 1975).
Grossly, neoplastic tissue had invaded and destroyed the entire orbital contents, ocular adnexa, other soft tissue and surrounding bones (Fig.
In the penguin, histologic examination revealed a marked infiltration of pleomorphic neoplastic lymphocytes in the kidneys, liver, lungs, adrenal glands, esophagus, proventriculus, and gizzard.
Metformin attenuated the increased insulin receptor activation associated with the high-energy diet and also led to increased phosphorylation of AMP kinase, two actions that would be expected to decrease neoplastic proliferation.
Busam (pathology, Sloan-Kettering Cancer Center, New York) introduces this text as a mid-level, practical one that emphasizes the clinical and histologic features required to make a diagnosis of the more common non-neoplastic and neoplastic conditions of the skin.
936) investigated the effects of arsenite on the inactivation of p53--a step implicated in the initiation of cancer--and neoplastic transformation of human embryo lung fibroblast (HELF) cells.
Adding complexity to the challenge of cancer in humans is the fact that cancer is not a single disease entity, but a myriad collection of neoplastic diseases that affect every cell type and tissue of the human body, resulting from various causes, including genetic factors and exogenous/environmental exposures (or some combination of these).
It may allow us to classify neoplastic and benign lesions in real time during colonoscopy, thus reducing the time and risk of procedures, with fewer polypectomies performed," she said, reporting the results of the prospective study among patients undergoing surveillance colonoscopy.