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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.

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An aberrant new growth of abnormal cells or tissues; a tumor.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Cytology diagnosis was divided into inflammatory and neoplastic lesions
PDA with neoplastic mucin cyst should be distinguished from IPMN with an associated invasive carcinoma.
The predominant population of neoplastic cells were polygonal with distinct cell borders, a moderate amount of eosinophilic to amphophilic lacy cytoplasm, and an irregularly round to oval nucleus possessing vesiculate chromatin and 1-2 prominent nucleoli.
(12) Abnormal cytokine release from the neoplastic T-cells are thought to be responsible for the systemic signs and symptoms and abnormal laboratory results.
Both non-neoplastic and neoplastic masses can develop within the ovaries, from the neonatal period to post-menopausal age.
A total of 1100 specimens were received during the study period and non-neoplastic lesions accounted for 99.4% of cases (1093 cases) and remaining 0.6% of cases (7 cases) were neoplastic lesions.
The present report describes a multifocal distribution of neoplastic nodules, the largest of which was in the right ventricle; however, MCEWEN (1994) reported that rhabdomyoma is more common in the left ventricle, but also it can be observed in the interventricular septum and the right ventricle (TANIMOTO & OHTSUKI, 1995).
Due to similar clinical presentations, there is confusion in the diagnosis of non-neoplastic and neoplastic lesions of ovary although it is diagnosed as a mass or cystic lesion on ultrasonography and hence removed prophylactically in routine oophorectomies and hysterectomies.
Microscopically, they are subdivided into intratubular or diffuse categories based on the organization of the neoplastic cells.
The company is currently focused on neoplastic diseases of the bone marrow including acute myeloid leukemia, myelodysplastic syndrome, polycythemia vera, myelofibrosis and essential thrombocythemia.