Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these cells to invade other tissues, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis. Metastasis is defined as the stage in which cancer cells are transported through the bloodstream or lymphatic system. Cancer may affect people at all ages, but risk tends to increase with age, due to the fact that DNA damage becomes more apparent in aging DNA. It is one of the principal causes of death in developed countries.
There are many types of cancer. Severity of symptoms depends on the site and character of the malignancy and whether there is metastasis. A definitive diagnosis usually requires the histologic examination of tissue by a pathologist. This tissue is obtained by biopsy or surgery. Most cancers can be treated and some cured, depending on the specific type, location, and stage. Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy. As research develops, treatments are becoming more specific for the type of cancer pathology. Drugs that target specific cancers already exist for several cancers. If untreated, cancers may eventually cause illness and death, though this is not always the case.
The unregulated growth that characterizes cancer is caused by damage to DNA, resulting in mutations to genes that encode for proteins controlling cell division. Many mutation events may be required to transform a normal cell into a malignant cell. These mutations can be caused by chemicals or physical agents called carcinogens, by close exposure to radioactive materials, or by certain viruses that can insert their DNA into the human genome. Mutations occur spontaneously, and may be passed down from one generation to the next as a result of mutations within germ lines. However, some carcinogens also appear to work through non-mutagenic pathways that affect the level of transcription of certain genes without causing genetic mutation.
Many forms of cancer are associated with exposure to environmental factors such as tobacco smoke, radiation, alcohol, and certain viruses. While some of these risk factors can be avoided or reduced, there is no known way to entirely avoid the disease.
Breast cancer is a cancer of the breast tissue. Worldwide, it is the most common form of cancer in females - affecting, at some time in their lives, approximately one out of nine to one out of thirteen women who reach age ninety in the Western world. It is the second most fatal cancer in women (after lung cancer), and the number of cases has significantly increased since the 1970s, a phenomenon partly blamed on modern lifestyles in the Western world.
Breast cancer is one of the oldest known forms of cancer tumors in humans. The oldest description of cancer (although the term cancer was not used) was discovered in Egypt and dates back to approximately 1600 BC. The Edwin Smith Papyrus describes 8 cases of tumors or ulcers of the breast that were treated by cauterization, with a tool called "the fire drill." The writing says about the disease, "There is no treatment."[4] At least one of the described cases is male. For centuries, physicians described similar cases in their practises, with the same sad conclusion. It wasn't until doctors achieved greater understanding of the circulatory system in the 17th century that they could establish a link between breast cancer and the lymph nodes in the armpit. The French surgeon Jean Louis Petit (1674-1750) and later the Scottish surgeon Benjamin Bell (1749-1806) were the first to remove the lymph nodes, breast tissue, and underlying chest muscle. Their successful work was carried on by William Stewart Halsted who started performing mastectomies in 1882. He became known for his Halsted radical mastectomy, a surgical procedure that remained popular up to the 1970s.
Epidemiologic risk factors and etiologyIt is important to have a model of causation of a disease in order to distinguish epidemiological risk factors or associations with disease, from the biological etiology and primary cause, secondary co-factors, and simple promoters of the disease. The first work on breast cancer epidemiology was done by Janet Lane-Claypon, who published a comparative study in 1926 of 500 breast cancer cases and 500 control patients of the same background and lifestyle for the British Ministry of Health.
Today, breast cancer, like other forms of cancer, is considered to be a result of damage to DNA. How this mechanism may occur comes from several known or hypothesized factors (such as exposure to ionizing radiation). Some factors lead to an increased rate of mutation (exposure to estrogens) and decreased repair (the BRCA1, BRCA2 and p53 genes). Although many epidemiological risk factors, and biological co-factors and promoters have been identified, the majority of breast cancer incidence remains unattributable, and the primary cause is unknown.
Dietary influences have been proposed and examined, but these are small effects, and do not distinguish differences in risk within populations, as well as they do between populations.
A significant environmental effect was revealed by the large difference in breast cancer incidence between countries and continents, and a migration effect which slowly increases the risk of breast cancer even across generations after migration from a country of lower incidence to a country of higher incidence, such as moving from China or Japan to the United States.
Humans are not the only mammal prone to breast cancer. Some strains of mice, namely the house mouse (Mus domesticus) are prone to breast cancer which is caused by infection with the mouse mammary tumour virus (MMTV or "Bittner virus" for its discoverer Hans Bittner), by random insertional mutagenesis. Suspicion of MMTV or other viruses in human breast cancer is controversial, and the idea is not generally accepted for lack of direct and definitive evidence. There is much more research in diagnosis and treatment of breast cancer than in its cause.
The probability of breast cancer rises with age but breast cancer tends to be more aggressive when it occurs in younger people. One type of breast cancer that is especially aggressive and disproportionately occurs in younger people is inflammatory breast cancer. It is initially staged as Stage IIIb or Stage IV. It also is unique because it often does not present with a lump so that it often is not detected by mammography or ultrasound. It presents with the signs and symptoms of a breast infection like mastitis.
Environmental causesAll women and men are at risk for breast cancer, regardless of hereditary factors. In fact, 85 to 90 percent of breast cancer incidences cannot be explained by inherited genetic predisposition. Other known risk factors and personal characteristics include personal or family history of breast cancer, high breast tissue density, earlier onset of menstruation (12 years or younger), later menopause (55 years or older), late first-term pregnancy (30 years or older), no children or no breast-feeding, early or recent use of oral contraceptives, more than four years use of hormone replacement therapy, postmenopausal obesity, alcohol consumption, exposures to secondhand cigarette smoke and exposure to ionizing radiation.
