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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 malignant epithelial tumor.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


1. any malignant tumour derived from epithelial tissue
2. another name for cancer
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Contrast-enhanced computed tomography (CECT) scanning is used in staging the renal cell carcinoma and also has the advantage of characterizing the cystic and solid nature of the mass as well as the extent of the tumour8.
Most gynecologic serous carcinomas involving fluid specimens expressed PAX8, although at a lower percentage rate than did those of the primary tumor, as reported in other studies.
Papillary carcinoma of thyroid (PTC) is the most common thyroid malignancy.
In the well differentiated squamous cell carcinomas there are few mitotic figures, atypical mitosis or multinucleate epithelial cells are rare.
Very aggressive endometrial carcinomas including high grade serous carcinoma are found to be less or non-responsive to usual chemotherapy.9
Papillary carcinomas may histopathologically show papillary, micropapillary, cribriform, reticular, and solid appearance.
Papillary thyroid carcinoma (PTC) is the most common malignant neoplasm of the thyroid [1].
Although acinic cell carcinomas do not typically show myoepithelial differentiation, they can rarely harbor a myoepithelial immunoprofile in the high-grade carcinomatous portions [18].
On the other hand, reduced p27Kip1 expression is correlated with a greater risk of recurrence in elderly patients.7 There have been many reports which suggest clinical characteristics and treatment for urothelial carcinoma in children but still there is debate on progression and prognosis.
Hrthle cell carcinoma accounts for about 3 percent of thyroid cancers and is a variant follicular carcinoma.
Histological examination revealed a high grade urothelial carcinoma with sarcomatoid differentiation.