Cancer

Cancer is a term used to refer to a wide variety of diseases that have in common uncontrolled cell proliferation. Cancers are generally classified by the cell or tissue type of origin. Groups of cells form "tissues", like the skin and the nerves, and all mature from forerunners that made up the outer layer of cells in the early embryo gastrula. Malignant growth entails both rapid cell division and loss of the inhibition for cells to contact and overgrow other cells, that is normally present. (more often involves lack of apoptosis and continued division, rather than actual increase in RATE of cell division)As clumps of cancer cells grow, then can form "tumors". Not all cancers form tumors. For instance, in most leukemias, the cancer cells are circulating through the blood, rather than forming discrete masses. Cancers, especially rapidly growing ones, can consume a great deal of energy, and can secrete various substances that cause a general decline in health.

Cancer can cause symptoms in a number of ways: by direct effect on the organ involved (i.e. a cough with lung cancer), by growing into a vital structure (i.e. prostate cancer obstructing the urethra), or by causing generalized malaise and anorexia. This last topic is less well understood.

When cancers are "early", they are usually small, when they are both late and widely disseminated, they generally involve a much greater portion of the body. That's one reason why early and limited cancers less obviously impair health, unless they happen to involve particularly vital regions of the body, like the brain. Since it is early (smaller) cancers that are most successfully treated, by and large, much of modern medicine has been devoted to finding means to diagnose malignancies early on, and public health campaigns have promoted education of citizens to early warning signs of the various kinds of cancer.

Although the origin of cancer in an epithelial tissue is strictly required for the most technically accurate use of the term, cancer, the word is often used, even by physicians and hospitals, to include all the diseases directly caused by malignant tumors and cells. For example, malignant tumors called sarcomas arise from abnormal muscle-type cells, and since these tissues are derived from mesothelium rather than from epithelium, that word sarcoma is used rather than cancer to name the tumor. Still, cancer centers and specialists include treatment of sarcoma in practice, despite the fact that sarcomas and cancers differ in the medical classification of malignant tumors. In other words, all types of malignant tumors are sometimes referred to as cancers, but one type of these malignancies: epithelial malignancies, are, even more strictly, known as cancers.

This introductory article will give a brief description of what a malignancy is, and how cells are thought to become malignant. That understanding is important as a basis to comprehend the medical and surgical treatment of cancers, and effective approaches to their prevention. After a general introduction to malignancies, major types of cancers (epithelial malignancies) are surveyed, with links provided for further information. The clinical emphasis is on human cancers, but references to cancers in other species of animals is also made. Although the frequencies and the aggresiveness of the various types of cancers vary according to species, generally, the basic biology of cancers is true for all species of vertebrate animals, including humans and domestic animals.

Oncology,Hematology and specialties that treat cancer

The two medical specialties that focus on malignancies are oncology and hematology. Oncologists are physicians who are fully trained in Internal Medicine and have further training in the treatment of malignant tumors, primarily solid tumors. Hematologists are also physicians who are fully trained in Internal Medicine, in their case further training is in disorders of the blood, including the bone marrow, which produces blood cells. Both hematologists and oncologists have advanced training in giving the drugs that inhibit cancer growth, called chemotherapy.

Some types of cancers and other malignancies are at least equally the province of other specialists, because of the part of the body they affect, or because the treatments they require, are the focus of those particular specialties. So, for example, radiation oncologists, who are trained in the use of external beam radiation and other kinds of radiation treatments, and surgeons who are specialists in the areas of the body that the cancer affects, like the breast or larynx, are important in cancer care, and depending on the type and extent of the cancer, may be the main physician directing the cancer patient's care. For several decades, the notion of a "team approach" has been embraced in the treatment of cancer. A team approach offers the support of an entire group of professionals, including the physicians of the specialties mentioned, nurses, social workers and others. The team also includes diagnostic physicians, like surgical pathologists and diagnostic radiologists who have special expertise in evaluation of the studies important for confirming and staging cancer.

Cancer is a malignancy

Historically, illnesses of human and animals that were progressive and fatal, and that involved tumors that destroyed flesh, were well known. Although the word cancer has been used to describe such conditions before the nature of malignancy was understood on a biological basis, today the term cancer is only used when malignant cells are present in the body. Many processes can cause the body to form masses (lumps), including infections, and scarring from trauma and burns. Since malignant cells can almost always be recognized under the microscope, if the tissue is properly prepared, a biopsy is virtually always required to make a firm diagnosis of cancer.

Types of Biopsies: Incisional & Excisional

There are two general types of biopsies: incisional and excisional. If an area is suspicious for a possible malignancy, and it is both small and accessible, the entire lesion is usually removed in the biopsy. So, for example, a small freckle of the skin that shows signs of possible melanoma would be removed completely, rather than simply sampled. On the other hand, if excision would entail extra risk to the patient or is better done in continuity with other structures of the body, such as lymph nodes or bone, then an incisional biopsy, in which only a relatively small portion of the lesion is removed, is a better choice.

Malignancy: How do malignant cells develop?

carcinogens are mutagens

"Cancer can be defined as a genetic disease at the cellular level" That's because the rate of cell division and the amount of differentiation of a cell are controlled by genes. When mature cells become more like embryonic cells, they are said to de-differentiate. Although this process is not thought to be the exact opposite of differentiation of cells, it does describe the loss of characteristics of mature cells that cancer cells undergo.

DNA repair

When DNA is damaged in normal cells, by such environmental processes as exposure to sunlight or by errors that occur in cell division, then, ideally, repairs are made and normal DNA is restored. If there are defects in the ability of a cell to repair DNA, this can lead to the daughters of that cell eventually becoming malignant. Since a small number of defects are expected to occur with each cell division, an inability to repair them can lead to more and more abnormalities in successive generations of cells.

Footnoted References

1) J. Larry Jameson, Peter Kopp:Chapter 56. Principles of Human Genetics. Harrison's Online Featuring the complete contents of Harrison's Principles of Internal Medicine, 16th Edition (Dennis L. Kasper, Eugene Braunwald, Anthony S. Fauci, Stephen L. Hauser, Dan L. Longo, J. Larry Jameson, and Kurt J. Isselbacher, Eds.)Copyright © 2005. Mcgraw-Hill's Access Medicine)

External links

Topics in Cancer - provided by the National Institutes of Health (USA) [1]

National Health Service site for general patient information (UK). Search for cancer in "questions" and "encyclopedia" [2]