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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 ?
Based on World Heath Organization (WHO) criteria, MCNs are defined as cystic epitheilal neoplasms composed of mucin producing columnar epithelium and an ovarian-type stroma which forms a band of densely packed stromal cells beneath the epithelium.
A review of the Malignant Neoplasms products under development by companies and universities/research institutes based on information derived from company and industry-specific sources.
Hematological and lymphoid neoplasms (groups I and II) showed evident improvements in survival for the recent 5-year periods.
The risk of colorectal cancer and benign neoplasms among those with chronic constipation remained "consistently high" after researchers controlled for potential confounding factors, including age, gender, family history of malignancies, and other nongastrointestinal morbidities, said Dr.
Among the patients that were not previously diagnosed with CRC or benign neoplasms prior to their index date, and after controlling for potential confounding factors including age, gender, family history of malignancies, and other non-gastrointestinal comorbidities, patients with CC were more at risk to develop CRC or benign neoplasms, the researchers said.
These are typical features for pathologic diagnosis of mucinous cystic neoplasm of the liver (MCN).
pylori infection and the presence of colonic neoplasms in 156,269 patients who had undergone both a colonoscopy and an esophagogastroduodenoscopy.
We illustrate the selection process for RCTs for prostatic neoplasms in 1997 (Fig.
These neoplasms are both synaptophysin positive, yet only pheochromocyoma is positive for chromogranin (2).
Solid and papillary epithelial neoplasm of the pancreas; differential considerations include: nonfunctioning islet cell tumor, pancreatoblastoma and complicated pseudocyst
Table 1: Causes of Death in Ireland, 2006 (CSO) Category of Disease Proportion Cancers and neoplasms 11.
This is a retrospective analysis of major salivary gland neoplasms in 127 patients who were treated between August 1988 and December 2004 (15 1/2 years) at Kalafong Hospital, Pretoria.