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Cancer is a group of diseases characterized by uncontrolled cell division and the ability of these cells to invade other tissues and spread to other areas of the body where the cells are not normally located (metastasis). Cancer is caused by damage to DNA (genetic material) through genetic and environmental factors, leading to aberrant growth regulation of cells. Cell multiplication (proliferation) is a normal physiologic process that occurs in almost all tissues and under many circumstances, such as response to injury, immune responses, or to replace cells that have died or have been shed as a part of their lifecycle (in tissues such as skin or the mucous membranes of the digestive tract). Normally the balance between proliferation and cell death is tightly regulated to ensure the integrity of organs and tissues. Mutations in DNA that lead to cancer appear to disrupt these orderly processes. The uncontrolled and often rapid proliferation of cells can lead to either a benign tumor or a malignant tumor (cancer). Benign tumors do not spread to other parts of the body or invade other tissues, and they are rarely a threat to life. Malignant tumors can invade other organs, spread to distant locations (metastasize) and become life-threatening.
Signs and symptomsWhile advanced cancer may cause pain, it is not always the first symptom. Roughly, cancer symptoms can be divided into three groups:
Every single item in the above list has a substantial differential diagnosis (it may be associated with unrelated diseases). Often, cancer is an unexpected finding during investigation for much more common symptoms, while others are diagnosed through screening (see below). Types of cancerCancers originate within a single cell. Hence, cancers can be classified by the type of cell in which it originates and by the location of the cell. Carcinomas originate in epithelial cells, e.g. skin, digestive tract or glands. Leukemia starts in the bone marrow stem cells. Lymphoma is a cancer originating in lymphatic tissue. Melanoma arises in melanocytes. Sarcoma begins in the connective tissue of bone or muscle. Teratoma begins within germ cells. Adult cancersAdult cancers are usually formed in epithelial tissues and are believed often to be the result of a long biological process related to the interaction of exogenous exposures with genetic and other endogenous characteristics among susceptible people. Examples include: bladder carcinoma, blood (and bone marrow) - hematological malignancies, leukemia, lymphoma, Hodgkin's disease, non-Hodgkin's lymphoma, multiple myeloma, brain tumor, breast cancer, cervical cancer, colorectal cancer - in the colon, rectum, anus, or appendix, esophageal cancer, endometrial cancer - in the uterus, hepatocellular carcinoma - in the liver, gastrointestinal stromal tumor (GIST), laryngeal cancer, lung cancer, mesothelioma - in the pleura or pericardium, oral cancer, osteosarcoma - in bones, ovarian cancer, pancreatic cancer, prostate cancer, renal cell carcinoma - in the kidneys, rhabdomyosarcoma - in muscles, skin cancer (including benign moles and dysplastic nevi), stomach cancer, testicular cancer, and thyroid cancer. Childhood cancersCancer can also occur in young children, particularly infants. Here, the aberrant genetic processes that fail to safeguard against the clonal proliferation of cells with unregulated growth potential occur very early in life and progress very quickly. The age of peak incidence of cancer in children occurs during the first year of life. Neuroblastoma is the most common infant malignancy, followed by the leukemias and the central nervous system cancers. Female infants and male infants have essentially the same overall cancer incidence rates, but white infants have substantially higher cancer rates than black infants for most cancer types. Relative survival for infants is very good for neuroblastoma, Wilms' tumor and retinoblastoma, but not for most other types of cancer. Childhood cancers include, from most frequently occurring to least: neuroblastoma, leukemia, central nervous system, retinoblastoma, Wilms' tumor, germ cell, soft tissue sarcomas, hepatic, lymphomas (such as Hodgkin's disease), epithelial. Cancer researchCancer research is the intense scientific effort to understand disease processes and discover possible therapies. While understanding of cancer has increased exponentially since the last decades of the 20th century, radically new therapies are only discovered and introduced gradually. Inhibitors of tyrosine kinases (imatinib and gefitinib) in the late 1990 were considered a major breakthrough; these interfere specifically with tumor-specific proteins. Computer simulations of cancer are helping scientists understand the nature of cancer and its relations to regulatory networks (see Pharmacodynamics ). Integrating in silico and in vivo approaches by studying minimal genomes for multicellular systems. Related LinksReferences
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