tumor

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n.

1. An abnormal growth of tissue resulting from uncontrolled, progressive multiplication of cells and serving no physiological function; a neoplasm.
2. A swollen part; a swelling.

[Middle English tumour, from Latin tumor, from tumēre, to swell.]

tumoral tu'mor·al or tu'mor·ous adj.

Literally, a swelling; in the past the term has been used in reference to any swelling of the body, no matter what the cause. However, the word is now being used almost exclusively to refer to a neoplastic mass, and the more general usage is being discarded.

A neoplastic mass or neoplasm is a pathological lesion characterized by the progressive or uncontrolled proliferation of cells. The cells involved in the neoplastic growth have an intrinsic heritable abnormality such that they are not regulated properly by normal methods. The stimulus which elicits this growth is not usually known.

It is common to divide tumors into benign or malignant. The decision as to which category a tumor should be assigned is usually based on information gained from gross or microscopic examination, or both. Benign neoplasms usually grow slowly, remain so localized that they cause little harm, and generally can be successfully and permanently removed. Malignant or cancerous neoplasms tend to grow rapidly, spread throughout the body, and recur if removed. Not all tumors which have been classified as benign are harmless to the host, and some can cause serious problems. Difficulties may occur as a result of mechanical pressure.

The cells of benign tumors are well differentiated. This means that the cells are very like the normal tissue in size, structure, and spatial relationship. The cells forming the tumor usually function normally. Cell proliferation usually is slow enough so that there is not a large number of immature cells. As the cellular mass increases in size, most benign tumors develop a fibrous capsule around them which separates them from the normal tissue. The cells of a benign tumor remain at the site of origin and do not spread throughout the body. Anaplasia (loss of differentiation) is not seen in benign tumors.

The cells of malignant tumors may be well differentiated, but most have some degree of anaplasia. Anaplastic cells tend to be larger than normal and are abnormal, even bizarre, in shape. The nuclei tend to be very large, and irregular, and they often stain darkly. Malignant tumors may be partially but never completely encapsulated. The cells of the cancer infiltrate and destroy surrounding tissue. They have the ability to metastasize; that is, cells from the primary tumor are disseminated to other regions of the body where they are able to produce secondary tumors called metastases.

In most cases the formation of a neoplasm is irreversible. It results from a permanent cellular defect which is passed on to daughter cells. Tumors should undergo medical appraisal to determine what treatment, if any, is needed.

Tumor suppressor genes are a class of genes which, when mutated, predispose an individual to cancer. The mutations result in the loss of function of the particular tumor suppressor protein encoded by the gene. Although this class of genes was named for its link to human cancer, it is now clear that these genes play a critical role in the normal development, growth, and proliferation of cells and organs within the human body. The protein product of many tumor suppressor genes constrains cell growth and proliferation so that these events occur in a controlled manner. Thus, these genes appear to act in a manner antagonistic to that of oncogenes, which promote cell growth and proliferation.

The retinoblastoma (RB), p53, and p16 genes are the best-understood tumor suppressors. Inactivating mutations in the RB gene have been observed in retinoblastomas, osteosarcomas (cancer of the bone), as well as cancers of the lung, breast, and bladder. The p16 mutations have been observed in cancers of the skin, lung, breast, brain, bone, bladder, kidney, esophagus, and pancreas. The tumor suppressor p53 is the most frequently mutated gene associated with the development of many different types of human cancer, including those of the breast, lung, and colon. It is also associated with the rare inherited disease, Li-Fraumeni syndrome. Affected individuals manifest an increased likelihood of breast carcinomas, soft tissue sarcoma, brain tumors, osteosarcoma, leukemia, and adrenocortical carcinoma. Like RB and p16, p53 has a role in cell cycle regulation. In addition, p53 functions in the cell's decision on whether to undergo programmed cell death (apoptosis). Deregulaed cell proliferation and escape from apoptosis appear to be two common pathways leading to tumor formation. See also Cancer (medicine); Gene; Gene action; Mutation; Oncology; Tumor viruses.

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n

A swelling. Through usage the term is now synonymous with neoplasm. See also neoplasm.

A swelling; one of the signs of inflammation. See also tumour.

An abnormal mass of new tissue growth that serves no function in the body. Tumors are usually classified as benign or malignant and are often caused by cancer.

1. swelling, one of the cardinal signs of inflammation; morbid enlargement.
2. neoplasm; a new growth of tissue in which cell multiplication is uncontrolled and progressive. A cancer.
Tumors are called also cancers or neoplasms, which means that they are composed of new and actively growing tissue. Their growth is faster than that of normal tissue, continuing after cessation of the stimuli that evoked the growth, and serving no useful physiological purpose.
Tumors are classified in a number of ways, one of the simplest being according to their origin and whether they are malignant or benign. Tumors of mesenchymal origin include fibroelastic tumors and those of bone, fat, blood vessels and lymphoid tissue. They may be benign or malignant (sarcoma). Tumors of epithelial origin may be benign or malignant (carcinoma); they are found in glandular tissue or such organs as the mammary gland, stomach, uterus or skin. Mixed tumors contain different types of cells derived from the same primary germ layer, and teratomas contain cells derived from more than one germ layer; both kinds may be benign or malignant.

• ACTH secreting t. — see corticotroph adenoma.
• benign t. — grows slowly, pushing aside normal tissue but not invading it. They are usually encapsulated, well-demarcated growths. They are not metastatic; that is, they do not form secondary tumors in other organs. Benign tumors usually respond favorably to surgical treatment and some forms of radiation therapy.
• t. blush — in cerebral arteriography, the pooling of contrast material where the blood–brain barrier has been interrupted.
• brown t. — a giant-cell granuloma produced in and replacing bone, occurring in osteitis fibrosa cystica and due to hyperparathyroidism.
• Burkitt's t. — see burkitt's lymphoma.
• button t. — histiocytoma.
• carotid body t. — see carotid body tumors.
• β cell t. — see insulinoma.
• t. clinical staging — see staging (2).
• connective tissue t. — any tumor arising from a connective tissue structure, e.g. a fibroma or fibrosarcoma.
• desmoid t. — see desmoid (2).
• t. enhancement — see tumor enhancement.
• erectile t. — cavernous hemangioma.
• false t. — structural enlargement due to extravasation, exudation, echinococcus or retained sebaceous matter.
• gastrin-secreting t. — see gastrinoma, zollinger–ellison syndrome.
• giant cell t. — see giant cell tumor.
• granulosa t., granulosa cell t. — a sex chord-stromal tumor, often referred to as granulosa–theca cell tumor, of the ovary originating in the cells of the cumulus oophorus. See also granulosa cell tumor.
• granulosa–theca cell t. — an ovarian tumor composed of granulosa (follicular) cells and theca cells; either form may predominate. See also granulosa–theca cell tumor.
• heterologous t. — one made up of tissue differing from that in which it grows.
• homoiotypic t., homologous t. — one made up of tissue resembling that in which it grows.
• Hürthle cell t. — a new growth of the thyroid gland composed wholly or predominantly of Hürthle cells. See also hürthle cell tumor.
• t. immunology — see tumor-specific antigen.
• t. immunotherapy — see immunotherapy.
• islet cell t. — a tumor of the islets of Langerhans, which may result in hyperinsulinism. See also insulinoma.
• t. lysis syndrome — a possible sequel to chemotherapy in which very rapid destruction of highly sensitive tumor cells results in release of large amounts of nucleic acid purines, lactate and uric acid which exceed renal and hepatic excretory mechanisms. Characterized by hyperkalemia, hyperphosphatemia, hypocalcemia, hyperuricemia and renal failure.
• malignant t. — composed of embryonic, primitive, or poorly differentiated cells. They grow in a disorganized manner and so rapidly that nutrition of the cells becomes a problem. For this reason necrosis and ulceration are characteristic of malignant tumors. They also invade surrounding tissues and are metastatic, initiating the growth of similar tumors in distant organs. See also cancer.
• mast cell t. — a benign, but occasionally malignant, local aggregation of mast cells forming a nodulous tumor. Mast cell tumors with diffuse visceral involvement are called systemic mastocytosis. See also mast cell tumor.
• mixed t. — one composed of more than one type of neoplastic tissue, as in mammary tumors.
• t. necrosis factor (TNF) — two related cytokines produced by macrophages (TNF-α) and some T cells (TNF-β) that are cytotoxic for tumor cells but not for normal cells and which exert a variety of other inflammatory effects. See also lymphotoxin.
• t.–node–metastases (TNM) classification — see TNM staging.
• non-neoplastic t. — tumor (1).
• organoid t. — teratoma.
• phantom t. — abdominal or other swelling not due to structural change.
• sand t. — psammoma.
• t.-specific antigen (TSA) — see tumor-specific antigen.
• true t. — neoplasm.

IN BRIEF: An abnormal new mass of tissue that serves no purpose.

To look at the cross-section of any plan of a big city is to look at something like the section of a fibrous tumor. — Frank Lloyd Wright (1867-1959)

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Dansk (Danish)
n. - knude, tumor

Français (French)
n. - tumeur

Deutsch (German)
n. - Tumor

Ελληνική (Greek)
n. - (παθολ.) όγκος, νεόπλασμα

Italiano (Italian)
tumore

Português (Portuguese)
n. - tumor (m)

Русский (Russian)
опухоль

Español (Spanish)
n. - tumor

Svenska (Swedish)
n. - tumör, svulst, växt

中文（简体）(Chinese (Simplified))
瘤, 肿块, 肿瘤

中文（繁體）(Chinese (Traditional))
n. - 瘤, 腫塊, 腫瘤

한국어 (Korean)
n. - 종기, 종양

日本語 (Japanese)
n. - ふくらみ, 腫瘍

עברית (Hebrew)
n. - ‮גידול (בגוף)‬

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