Tumor

Tumor or tumour is an irregular growth or mass of tissue. A tumor can be either malignant or benign. Almost all tumors are examples of neoplasia, although certain developmental malformations or inflammatory masses may occasionally be referred to as tumors.

Neoplastic tumors are caused by mutations in DNA of cells, which interfere with a cell's capability to regulate and limit cell division. An accumulation of mutations is needed for a tumor to emerge. Mutations that activate oncogenes or repress tumor suppressor genes can eventually lead to tumors. Cells have mechanisms that repair DNA and other mechanisms that cause the cell to destroy itself by apoptosis if DNA damage gets too severe. Mutations that repress the genes for these mechanisms can also ultimately guide to cancer. A mutation in one oncogene or one tumor repressor gene is usually not enough for a tumor to occur. A combination of a number of mutations is essential.