Cancer is a class of diseases in which of cells display uncontrolled growth (divison beyond the normal limits), invasion (instrusion on and destruction of adjacent tissues), and sometimes metastasis (spread to other locations in the body via lymph or blood). These three malignant properties of cancers differentiate them from benign tumors, which are self - limited, do not invade or metastasize. Most cancers form a tumor but some, like leukimia, do not.
Cancer may affect people at all ages, even fetuses, but the risk for most varieties increases with age. Cancer causes about 13% of all deaths. According to the American Cancer Society, 7.6 million people died from cancer in the world during 2007.
Nearly all cancers are caused by abnormalities in the genetic material of the transformed cells. These abnormalities may be due to the effects of carcinogens, such as tobacco smoke, radiation, chemicals or infectious agents. Other cancer - promoting genetic abnormalities may be randomly acquired through errors in DNA replication or are inherited and thus present in all cell from birth. The heritability of cancers are usually affected by complex interactions between carcinogens and the host's genome.
Diagnosis usually requires the histologic examination of a tissue biopsy specimen by a pathologist, although the initial indication of malignancy can be symptoms or radiographic imaging abnormalities. Most cancers can be treated and some cured, depending on the spesific type, location and stage. Once diagnosed, cancer is usually treated with combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for different varieties of cancer. There has been significant progress in the development of targeted therapy drugs that act specifically on detectable moleculer abnormalities in certain tumors and which minimize damage to normal cells. The prognosis of cancer patients is most influenced by the type of cancer, as well as the stage, or extent of the disease. In addition, histologic grading and the presence of specific molecular markers can also be useful in estabilishing prognosis, as well as in determining individual treatments.