August 10, 2011

What Is Cancer

Cancer /ˈkænsər/ ( listen) (medical term: malignant neoplasm) is a large, heterogeneous class of diseases in which a group of cells display uncontrolled growth, invasion that intrudes upon and destroys adjacent tissues, and often metastasizes, wherein the tumor cells spread to other locations in the body via the lymphatic system or through the bloodstream. These three malignant properties of cancer differentiate malignant tumors from benign tumors, which do not grow uncontrollably, directly invade locally, or metastasize to regional lymph nodes or distant body sites like brain, bone, liver, or other organs.

Researchers divide the causes of cancer into two groups: those with an environmental cause, and those with a hereditary genetic cause. Cancer is primarily an environmental disease, though genetics influence the risk of some cancers.[1] Common environmental factors leading to cancer include: tobacco use, poor diet and obesity, infection, radiation, lack of physical activity, and environmental pollutants.[1] These environmental factors cause or enhance abnormalities in the genetic material of cells.[2] Cell reproduction is an extremely complex process that is normally tightly regulated by several classes of genes, including oncogenes and tumor suppressor genes. Hereditary or acquired abnormalities in these regulatory genes can lead to the development of cancer. A small percentage of cancers, approximately five to ten percent, are entirely hereditary.

The presence of cancer can be suspected on the basis of clinical signs and symptoms, or findings after medical imaging. Definitive diagnosis of cancer, however, requires the microscopic examination of a biopsy specimen. Most cancers can be treated, with the most important modalities being chemotherapy, radiotherapy and surgery. The prognosis in cancer cases can be greatly influenced by the type and location of the cancer and the extent of disease. While cancer can affect people of all ages, and a few types of cancer are more common in children than in adults, the overall risk of developing cancer generally increases with age, at least up to age 80-85 yr. In 2007, cancer caused about 13% of all human deaths worldwide (7.9 million). Rates are rising as more people live to an old age and as mass lifestyles changes occur in the developing world.[3]

Cancers are classified by the type of cell that the tumor resembles and is therefore presumed to be the origin of the tumor. These types include:

* Carcinoma: Cancers derived from epithelial cells. This group includes many of the most common cancers, particularly in the aged, and include nearly all those developing in the breast, prostate, lung, pancreas, and colon.
* Sarcoma: Cancers arising from connective tissue (i.e. bone, cartilage, fat, nerve), each of which develop from cells originating in mesenchymal cells outside the bone marrow.
* Lymphoma and leukemia: These two classes of cancer arise from hematopoietic (blood-forming) cells that leave the marrow and tend to mature in the lymph nodes and blood, respectively.
* Germ cell tumor: Cancers derived from pluripotent cells, most often presenting in the testicle or the ovary (seminoma and dysgerminoma, respectively.
* Blastoma: Cancers derived from immature "precursor" cells or embryonic tissue. These are also commonest in children.[citation needed]

Cancers are usually named using -carcinoma, -sarcoma or -blastoma as a suffix, with the Latin or Greek word for the organ or tissue of origin as the root. For example, cancers of the liver parenchyma arising from malignant epithelial cells is called hepatocarcinoma, while a malignancy arising from primitive liver precursor cells is called a hepatoblastoma, and a cancer arising from fat cells is called a liposarcoma. For some common cancers, the English organ name is used. For example, the most common type of breast cancer is called ductal carcinoma of the breast. Here, the adjective ductal refers to the appearance of the cancer under the microscope, which suggests that it has originated in the milk ducts.

Benign tumors (which are not cancers) are named using -oma as a suffix with the organ name as the root. For example, a benign tumor of smooth muscle cells is called a leiomyoma (the common name of this frequently occurring benign tumor in the uterus is fibroid). Confusingly, some types of cancer also use the -oma suffix, examples including melanoma and seminoma.

Some types of cancer are named for the size and shape of the cells under a microscope, such as giant cell carcinoma, spindle cell carcinoma, and small cell carcinoma.

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