Cancer

Cancer is a class of diseases characterized by uncontrolled cell division and the ability of these cells to invade other tissues, either by direct growth into adjacent tissue (invasion) or by migration of cells to distant sites. This unregulated growth is caused by damage to DNA, resulting in mutations to vital genes that control cell division, among other functions. One or more of these mutations, which can be inherited or acquired, can lead to uncontrolled cell division and tumor formation. A tumor refers to any abnormal mass of tissue, but may be either malignant (cancerous) or benign (noncancerous). Only malignant tumors are capable of invading other tissues or metastasizing.  Cancer can cause many different symptoms, depending on the site and character of the malignancy and whether there is metastasis. A definitive diagnosis usually requires the microscopic examination of tissue obtained by biopsy. Once diagnosed, cancer is usually treated with surgery, chemotherapy and/or radiation.
If untreated, most cancers eventually cause death; cancer is one of the leading causes of death in developed countries. Most cancers can be treated and many cured, especially if treatment begins early. Many forms of cancer are associated with environmental factors, which may be avoidable.  Most cancers are initially recognized either because signs or symptoms appear or through screening. Neither of these lead to a definitive diagnosis, which usually requires a biopsy. Some cancers are discovered accidentally during medical evaluation of an unrelated problem. Roughly, cancer symptoms can be divided into three groups.  Local symptoms: unusual lumps or swelling (tumor), hemorrhage (bleeding), pain and/or ulceration. Compression of surrounding tissues may cause symptoms such as jaundice. Symptoms of metastasis (spreading): enlarged lymph nodes, cough and hemoptysis, hepatomegaly (enlarged liver), bone pain, fracture of affected bones and neurological symptoms. Although advanced cancer may cause pain, it is usually not the first symptom. Systemic symptoms: weight loss, poor appetite and cachexia (wasting), excessive sweating, anemia and specific paraneoplastic phenomena, i.e. specific conditions that are due to an active cancer, such as thrombosis or hormonal changes.