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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 ?
Hematological and lymphoid neoplasms (groups I and II) showed evident improvements in survival for the recent 5-year periods.
The differential diagnosis includes simple cysts, echinococcal cysts, liver abscesses, cystic degeneration of a liver neoplasm, Caroli's disease, posttraumatic cysts, and polycystic diseases.
SAN DIEGO -- Patients with Helicobacter pylori infection face a significantly increased risk for developing colonic neoplasms, according to what is believed to be the largest investigation of the association.
Melan-A is an antigen recognized by cytotoxic T-cells initially thought to be restricted to melanocytic tumors, but later on recognized to be present on steroid hormone-producing neoplasms including adrenocortical tumors (2).
3,4) Thus, this tumor is probably best classified as a neoplasm of borderline malignant potential.
Described as the "largest population-based study of absolute and relative risk of second malignant neoplasms," the study involved 16,540 survivors whose records were found in 13 cancer registries in New South Wales, Australia; British Columbia, Manitoba, and Saskatchewan, Canada; the Nordic countries; Singapore; Slovenia; Zaragoza, Spain; and Scotland.
Interestingly, none of these cysts had accumulated more than a single mutation, whereas sequencing of IPMNs reveals about 26 mutations per neoplasm, with mutations in KRAS, GNAS, and RNF43 observed most frequently.
Keywords: Angiosarcoma, Neck nodes, Bony metastasis, Vascular neoplasm.
5,6) once thought to be a common paediatric neoplasm was observed in only one case.