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neoplasm or tumor, 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., cancers, 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 leukemias 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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A benign tumor of glandular origin and structure.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Parathyroid adenomas can be successfully localized with a pre-operative Sestamibi scan.
During the study period, 5,811 adenomas were observed in the men compared to 8,116 in the women.
But it's not been clear whether yogurt intake might also be associated with a lower risk of pre-cancerous growths, known as adenomas.
Histologically, they may present as multiple hamartomatous polyps of differing types featuring juvenile-type polyps, ganglioneuromas, lipomas, and adenomas. (37) If a PTEN mutation is identified, the risk of adenocarcinoma of breast, thyroid, and endometrium appears increased; however, an excess risk of GI cancer has not been well established.
While EPA by contrast did not conclusively reduce the mean total number of adenomas per participant, it did reduce the number of adenomas in the left-sided colon, with an IRR of 0.75 (95% CI, 0.60-0.94).
A newly published article in Lancet, entitled "EPA and aspirin, alone and in combination, for the prevention of colorectal adenomas (seAFOod Polyp Prevention trial): a multicentre, randomised, double-blind, placebo-controlled, 2x2 factorial trial," researched the effect of EPA and aspirin for the prevention of colorectal adenomas (5).
In current US practice, many gastroenterologists perform follow-up colonoscopy about five years after removing one or two nonadvanced adenomas during a screening colonoscopy.
Lipid-rich adenomas are also easily diagnosed on chemical shift MRI, using breath-held dual-echo T1-weighted, gradient-recalled echo (GRE), acquired in-phase and opposed phase.
"An oral, delayed-release, methylene blue tablet taken during the standard bowel preparation for colonoscopy has the potential to increase the adenoma detection rate and could assist in the early detection and prevention of colorectal cancer," according to Michael B.
Exclusive endoscopic transsphenoidal resection of pituitary adenomas when compared to the traditional microscopic approach is found to be safer and more efficacious.6 Advantages of this approach are; it provides a larger field of vision of the sella and surrounding structures, better understanding of anatomy, increased working field and reduced injuries to nasal cavity.6 Systematic reviews and international data have shown that the endoscopic approach is associated with a higher rate of gross total resection, decreased hospital stay and reduced observed postoperative complications.7
The present study was done to evaluate the cytomorphological features of pleomorphic adenomas with an emphasis on differential diagnoses, challenges encountered during the diagnosis and addressing potential pitfalls.
Some studies have shown that loss of adhesion protein expression may be involved in the pathogenesis of pituitary adenomas and contribute to tumor aggressiveness and invasiveness (4-7).