Neoplasms may be benign (not cancer) or malignant (cancer).
A neoplasmis a type of abnormal and excessive growth, called neoplasia, of tissue. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and it persists growing abnormally, even if the original trigger is removed. This abnormal growth usually (but not always) forms a mass. When it forms a mass, 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. 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 clonal – 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 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).
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. Recently, 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.
DNA damage is considered to be the primary underlying cause of malignant neoplasms known as cancers. Its central role in progression to cancer is illustrated in the figure in this section, in the box near the top. (The central features of DNA damage, epigenetic alterations and deficient DNA repair in progression to cancer are shown in red.) DNA damage is very common. Naturally occurring DNA damages (mostly due to cellular metabolism and the properties of DNA in water at body temperatures) occur at a rate of more than 60,000 new damages, on average, per human cell, per day. UV light from solar radiation causes DNA damage that is important in melanoma. Individuals with a germ line mutation causing deficiency in any of 34 DNA repair genes (see article DNA repair-deficiency disorder) are at increased risk of cancer. Some germ line mutations in DNA repair genes cause up to 100% lifetime chance of cancer (e.g., p53 mutations).
Journal of Clinical Oncology and Cancer Research,