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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 ?
Although a strong protective effect of colonoscopy from colorectal neoplasms has been established through previous studies, our results add to the evidence that this effect is much stronger in, if not confined to, the left colon and rectum, at least in the community setting," concluded Dr.
The prevalence of colorectal neoplasms in patients with CAD in their study was nearly three times as high as that reported in the general population in either Hong Kong or the United States, investigators reported.
11) Almost all renal cell neoplasms are positive for broad-spectrum CK (pancytokeratin); however, some commonly used broad-spectrum CK antibodies, such as AE1/AE3, lack the specificity for CK18, a low-molecular-weight CK expressed in all simple epithelia and commonly paired with CK8.
Cystic neoplasms of the adult kidney are a diverse group of pathologically distinct tumors with variable clinico-biological profiles.
Mucinous neoplasms of the appendix are classified on a spectrum from benign to malignant based upon certain features during histologic examination.
On review of these 6 cases, all 6 were found to have some nuclear features suggestive of papillary carcinoma (pale chromatin, nuclear grooves, irregular nuclear outline) in addition to features suggestive of either follicular or Hurthle cell neoplasms, which was why they were not classified as incidental tumors.
The 16 chapters cover embryological development; surgical anatomy; the historical perspective; classification; diagnosis; non-neoplastic diseases; the etiology and pathogenesis of tumors; the incidence, histogenesis, and surgical pathology of salivary gland neoplasms; the surgical management of parotid neoplasms, submandibular and sublingual neoplasms, and minor salivary gland neoplasms; complications of surgery; and chemotherapy and radiotherapy.
Neoplasms arising in urinary bladder diverticulae are uncommon, but not rare.
Chronic constipation may predispose affected patients to developing colorectal cancer and benign neoplasms, according to an analysis of data from a large retrospective U.
Their study investigated the prevalence and incidence of colorectal cancer and benign neoplasms in 28,854 patients with chronic constipation (CC) and 86,562 controls without CC that were identified from a large retrospective U.
Mucinous cystic neoplasms of the liver: a clinicopathological study and comparison with intraductal papillary neoplasms of the bile duct.