<unk>  is a group of diseases in which cells are aggressive (grow and divide without respect to normal limits), invasive (invade and destroy adjacent tissues), and sometimes metastatic (spread to other locations in the body). These three malignant properties of<unk> s differentiate them from benign tumors, which are self-limited in their growth and don't invade or metastasize (although some benign tumor types are<unk> pable of becoming malignant).<unk>  may affect people at all ages, even fetuses, but risk for the more common varieties tends to increase with age.<unk> <unk> uses about 13% of all deaths. According to the American<unk>  Society, 7.6 million people died from<unk>  in the world during 2007. Apart from humans, forms of<unk>  may affect other animals and plants.
Nearly all<unk> s are<unk> used by abnormalities in the genetic material of the transformed cells. These abnormalities may be due to the effects of<unk> rcinogens, such as tobacco smoke, radiation, chemicals, or infectious agents. Other<unk> -promoting genetic abnormalities may be randomly acquired through errors in DNA replication, or are inherited, and thus present in all cells from birth. Complex interactions between<unk> rcinogens and the host genome may explain why only some develop<unk>  after exposure to a known<unk> rcinogen. New aspects of the genetics of<unk>  pathogenesis, such as DNA methylation, and microRNAs are increasingly being recognized as important.
Genetic abnormalities found in<unk>  typically affect two general classes of genes.<unk> -promoting oncogenes are often activated in<unk>  cells, giving those cells new properties, such as hyperactive growth and division, protection against programmed cell death, loss of respect for normal tissue boundaries, and the ability to become established in diverse tissue environments. Tumor suppressor genes are often inactivated in<unk>  cells, resulting in the loss of normal functions in those cells, such as accurate DNA replication, control over the cell cycle, orientation and adhesion within tissues, and interaction with protective cells of the immune system.<unk>  is usually classified according to the tissue from which the<unk> ous cells originate, as well as the normal cell type they most resemble. These are location and histology, respectively. A definitive diagnosis usually requires the histologic examination of a tissue biopsy specimen by a pathologist, although the initial indication of malignancy<unk> n be symptoms or radiographic imaging abnormalities. Most<unk> s<unk> n be treated and some cured, depending on the specific type, location, and stage. Once diagnosed,<unk>  is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for different varieties of<unk> . There has been significant progress in the development of targeted therapy drugs that act specifically on detectable molecular abnormalities in certain tumors, and which minimize damage to normal cells. The prognosis of<unk>  patients is most influenced by the type of<unk> , as well as the stage, or extent of the disease. In addition, histologic grading and the presence of specific molecular markers<unk> n also be useful in establishing prognosis, as well as in determining individual treatments.
Cancer
Tumor
Disease
Cardiovascular disease
Skin cancer
Endocrine diseases
Skin disease
Bone cancer