Neoplasms

A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists in growing abnormally, even if the original trigger is removed. This abnormal growth usually forms a mass, when it may be called a tumor.

ICD-10 classifies neoplasms into four main groups: benign neoplasms, in situ neoplasms, malignant neoplasms, and neoplasms of uncertain or unknown behavior. Malignant neoplasms are also simply known as cancers and are the focus of oncology.

Prior to the abnormal growth of tissue, as neoplasia, cells often undergo an abnormal pattern of growth, such as metaplasia or dysplasia. However, metaplasia or dysplasia does not always progress to neoplasia and can occur in other conditions as well. The word is from Ancient Greek 'new' and 'formation, creation'.

Types

A neoplasm can be benign, potentially malignant, or malignant (cancer).
* Benign tumors include uterine fibroids, osteophytes and melanocytic nevi (skin moles). They are circumscribed and localized and do not transform into cancer.
* Potentially-malignant neoplasms include carcinoma in situ. They are localised, do not invade and destroy but in time, may transform into a cancer.
* Malignant neoplasms are commonly called cancer. They invade and destroy the surrounding tissue, may form metastases and, if untreated or unresponsive to treatment, will generally prove fatal.
* Secondary neoplasm refers to any of a class of cancerous tumor that is either a metastatic offshoot of a primary tumor, or an apparently unrelated tumor that increases in frequency following certain cancer treatments such as chemotherapy or radiotherapy.
* Rarely there can be a metastatic neoplasm with no known site of the primary cancer and this is classed as a cancer of unknown primary origin.

Clonality

Neoplastic tumors are often heterogeneous and contain more than one type of cell, but their initiation and continued growth is usually dependent on a single population of neoplastic cells. These cells are presumed to be monoclonal – that is, they are derived from the same cell, and all carry the same genetic or epigenetic anomaly – evident of clonality. For lymphoid neoplasms, e.g. lymphoma and leukemia, clonality is proven by the amplification of a single rearrangement of their immunoglobulin gene (for B cell lesions) or T cell receptor gene (for T cell lesions). The demonstration of clonality is now considered to be necessary to identify a lymphoid cell proliferation as neoplastic.

It is tempting to define neoplasms as clonal cellular proliferations but the demonstration of clonality is not always possible. Therefore, clonality is not required in the definition of neoplasia.

Neoplasm vs. tumor

The word ''tumor'' or ''tumour'' comes from the Latin word for ''swelling'', which is one of the cardinal signs of inflammation. The word originally referred to any form of swelling, neoplastic or not. In modern English, ''tumor'' is used as a synonym for neoplasm (a solid or fluid-filled cystic lesion that may or may not be formed by an abnormal growth of neoplastic cells) that appears enlarged in size.
Some neoplasms do not form a tumor - these include leukemia and most forms of carcinoma in situ. ''Tumor'' is also not synonymous with ''cancer.'' While cancer is by definition malignant, a tumor can be benign, precancerous, or malignant.

The terms ''mass'' and ''nodule'' are often used synonymously with ''tumor''. Generally speaking, however, the term ''tumor'' is used generically, without reference to the physical size of the lesion. More specifically, the term ''mass'' is often used when the lesion has a maximal diameter of at least 20 millimeters (mm) in greatest direction, while the term '' nodule'' is usually used when the size of the lesion is less than 20 mm in its greatest dimension (25.4 mm = 1 inch).

Causes

Tumors in humans occur as a result of accumulated genetic and epigenetic alterations within single cells, which cause the cell to divide and expand uncontrollably. A neoplasm can be caused by an abnormal proliferation of tissues, which can be caused by genetic mutations. Not all types of neoplasms cause a tumorous overgrowth of tissue, however (such as leukemia or carcinoma in situ) and similarities between neoplasmic growths and regenerative processes, e.g., dedifferentiation and rapid cell proliferation, have been pointed out.

Tumor growth has been studied using mathematics and continuum mechanics. Vascular tumors such as hemangiomas and lymphangiomas (formed from blood or lymph vessels) are thus looked at as being amalgams of a solid skeleton formed by sticky cells and an organic liquid filling the spaces in which cells can grow. Under this type of model, mechanical stresses and strains can be dealt with and their influence on the growth of the tumor and the surrounding tissue and vasculature elucidated. Recent findings from experiments that use this model show that active growth of the tumor is restricted to the outer edges of the tumor and that stiffening of the underlying normal tissue inhibits tumor growth as well.

Benign conditions that are ''not'' associated with an abnormal proliferation of tissue (such as sebaceous cysts) can also present as tumors, however, but have no malignant potential. Breast cysts (as occur commonly during pregnancy and at other times) are another example, as are other encapsulated glandular swellings (thyroid, adrenal gland, pancreas).

Encapsulated hematomas, encapsulated necrotic tissue (from an insect bite, foreign body, or other noxious mechanism), keloids (discrete overgrowths of scar tissue) and granulomas may also present as tumors.

Discrete localized enlargements of normal structures (ureters, blood vessels, intrahepatic or extrahepatic biliary ducts, pulmonary inclusions, or gastrointestinal duplications) due to outflow obstructions or narrowings, or abnormal connections, may also present as a tumor. Examples are arteriovenous fistulae or aneurysms (with or without thrombosis), biliary fistulae or aneurysms, sclerosing cholangitis, cysticercosis or hydatid cysts, intestinal duplications, and pulmonary inclusions as seen with cystic fibrosis. It can be dangerous to biopsy a number of types of tumor in which the leakage of their contents would potentially be catastrophic. When such types of tumors are encountered, diagnostic modalities such as ultrasound, CT scans, MRI, angiograms, and nuclear medicine scans are employed prior to (or during) biopsy or surgical exploration/excision in an attempt to avoid such severe complications.

Malignant neoplasms

DNA damage

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