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.
X-linked endothelial corneal dystrophy (XECD) is a rare form of corneal dystrophy described first in 2006, based on a 4-generation family of 60 members with 9 affected males and 35 trait carriers, which led to mapping the XECD locus to Xq25. It manifests as severe corneal opacification or clouding, sometimes congenital, in the form of a ground glass, milky corneal tissue, and moon crater-like changes of corneal endothelium. Trait carriers manifest only endothelial alterations resembling moon craters.As of December 2014, the molecular basis for this disease remained unknown, although 181 genes were known to be within the XECD locus, of which 68 were known to be protein-coding. References


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