MT training : cancer medicine

Cancer is a disease characterized by unrestrained and excessive multiplication of body cells. It may occur in any body tissue and at any age, although cancer is found most frequently in older people. Cancerous cells accumulate as growths called malignant tumors, which penetrate, compress, and ultimately destroy the surrounding normal tissue. In addition to their local growth, cancerous cells also have the ability to spread throughout the body by way of the bloodstream or lymphatic vessels. In most patients, the spread of cancers from their site of origin to distant organs is responsible for causing death.

Tumors

Tumors (also called neoplasms) are masses, or growths, that arise from normal tissue. They may be either

1. malignant (progressive and life-threatening)

2. benign (non progressive and not life-threatening).

Differences between benign and malignant tumors.

*Benign tumors*	*Malignant tumor*
1. grow slowly	cells multiply rapidly.
2. often encapsulated (contained within a fibrous capsule or cover),sothat the tumor cells do not invade thethe surrounding tissue	growth is characteristically invasive and infiltrative, extending beyond the tissue or origin into adjacent organs.
3. Composed of highly organized and Specialized (differentiated) cells, which closely resemble normal, mature tissue.	composed of cancerous cells that resemble primitive or embryonic cells, that do not have the capacity for mature cellular function, this characteristic of malignant tumor is called anaplasia.
4. Cells do not spread to form secondary tumor masses in other places in the Body.	Malignant tumors, however detach themselves from the primary (original) tumor site, travel through the bloodstream and lymphatic system, and establish a new tumor site at a distant region within the body. This secondary growth is called a metastasis.

Carcinogen’s

Agents from the environment-such as chemicals and drugs, radiation, and viruses- can cause changes in DNA and thus produce cancer. These environmental agents are called carcinogens.

§ Chemical carcinogens are found in a variety of products and drugs including hydrocarbons (in cigarette, cigar, and pipe smoke and automobile exhaust), insecticides, dyes, industrial chemicals etc.,

§ Radiation, (whatever its source)---sunlight, x-rays, radioactive substances, nuclear fission - is a wave of energy. When it interacts with DNA it cause breaks or mutations that lead to cancer. Thus, leukemia is an occupational hazard of radiologists, who are routinely exposed to x-rays. There is also a high incidence of leukemia and other cancers among survivors of atomic bomb explosions, as in Hiroshima and Nagasaki. Ultraviolet radiation given of by the sun can cause skin cancer (basal cell carcinoma, squamous cell carcinoma, and melanoma), especially in persons with lightly pigmented, or fair skin.

§ Some viruses have been proved to be carcinogenic in a variety of animals. For example, the human T cell leukemia virus (HTVL) causes a form of leukemia in adults. A related virus, the HTV (human immunodeficiency virus), causes AIDS (acquired immunodeficiency syndrome). Other viruses have been implicated as the cause of cervical cancer (papilloma virus) and Burkitt’s lymphoma (Epstein-Barr virus composed of DNA). In addition to transmission of cancer by whole viruses, pieces of viral DNA (called viral oncogenes) or similar broken or dislocated pieces of human DNA (called cellular oncogenes) can cause normal cells to become malignant if they are activated by mutations. An oncogene is a piece of DNA whose activation is associated with the conversion of normal cells into cancer cells.

Heredity

Causes of cancer not only comes from the environment but also originate within the body. Susceptibility to some forms of cancer is transmitted from parents to offspring through defects in the DNA of the egg and sperm cells.

Examples of known inherited cancers are

§ retinoblastoma (tumor of the retina of the eye)

§ xeroderma pigmentosum (tumor on skin exposed to sunlight),

§ certain types of malignant melanoma, and

§ polyposis coli syndrome (polyps that grow in the colon and rectum).

1. Classification

About half of all cancer deaths are caused by malignancies that originate in lung, breast or colon. However, in all there are more than 100 distinct types of cancer, each having a unique set of symptoms and requiring a specific type of therapy. It is possible to divide these specific types of cancer into three broad groups on the basis of histogenesis that is, by identifying the particular tissue (hist/o) from which the tumor cells arise (-genesis). These major groups are called carcinomas, sarcomas, and mixed-tissue tumors.

Carcinomas

Carcinomas, the largest group, are solid tumors that are derived from epithelial tissue that lines external and internal body surfaces, including skin, glands, and digestive, urinary and reproductive organs. Approximately 90 percent of all malignant neoplasm’s are carcinomas.

· Benign tumors of epithelial origin are usually designated by adding the suffix -oma to the type of tissue in which the tumor occurs. For example, a gastric adenoma is a benign tumor of the glandular (aden/o) epithelial cells lining to the stomach.

Malignant tumors of epithelial origin are named by using carcinoma added to the type of tissue in which the tumor occurs. Thus, a gastric carcinoma is a cancerous tumor arising from glandular cells lining the stomach.

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