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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 ?
All neoplastic lesions were unilateral except for 3 cases of benign serous cystadenoma, which were bilateral.
Based on histopathological diagnosis biopsies were divided into seven groups, viz, eczema-dermatitis, papulosquamous disorders, infectious disorders, blistering disorders, neoplastic lesions, degenerative diseases and miscellaneous lesions.
Results: There were 264 (95%) nonneoplastic GBPs and 14 (5%) neoplastic GBPs.
Conclusion: This study gives spectrum of non-neoplastic and neoplastic CNS lesions.
Stromal reactive T-cells which are dominant in the neoplasm, are regarded as 'host immune response' against neoplastic clone, and therefore with this feature, it resembles Hodgkin's disease.
Cysts with neoplastic features are recommended for indefinite surveillance, even though there are few or no data on their natural history and malignant potential beyond 5-10 years, they added.
Lymphosarcoma is one of the most common neoplastic processes affecting birds.
Table 1: Distribution of non-neoplastic and neoplastic thyroid lesions (n=105).
8 Both the neoplastic cells and stroma show positive immunostaining thus indicating it is involved in carcinogenesis and might be a novel prognostic factor in some malignant tumors.
12) Abnormal cytokine release from the neoplastic T-cells are thought to be responsible for the systemic signs and symptoms and abnormal laboratory results.
In this study, we have quantified immune cell infiltration (based on microscopy performed on H and E stained tissues) in pre-neoplastic, neoplastic and control breast tissues.