Breast cancer is a cancer of 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 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.
Anatomy of the Breasts
The breasts sit on the chest muscles that cover the ribs. Each breast is made of 15 to 20 lobes. Lobes contain many smaller lobules. Lobules contain groups of tiny glands that can produce milk. Milk flows from the lobules through thin tubes called ducts to the nipple. The nipple is in the center of a dark area of skin called the areola. Fat fills the spaces between the lobules and ducts.
The breasts also contain lymph vessels. These vessels lead to small, round organs called lymph nodes. Groups of lymph nodes are near the breast in the axilla (underarm), above the collarbone, in the chest behind the breastbone, and in many other parts of the body. The lymph nodes trap bacteria, cancer cells, or other harmful substances.
History of breast cancer
Breast cancer is one of the oldest known forms of cancer tumors. The oldest description of cancer (although the term cancer was not used) was discovered in Egypt and dates back to approximately 1600 BCE. 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." 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.
Types of breast cancer
- DCIS: Ductal Carcinoma in Situ
- LCIS: Lobular Carcinoma in Situ
- Invasive ductal carcinoma
- Invasive lobular carcinoma
- Inflammatory breast cancer
- Paget's disease
Epidemiologic risk factors and etiology
It 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.
contradictory The risk of getting breast cancer increases with age. For someone who lives to the age of 90, the chances of getting breast cancer is about 14.3% or one in seven during their lifetime.
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.
Two genes, BRCA1 and BRCA2, have been linked to the rare familial form of breast cancer Template:Cite needed. People in families expressing mutations in these genes have a much higher risk of developing breast cancer than women who do not. Not all people who inherit mutations in these genes will develop breast cancer. Together with Li-Fraumeni syndrome (p53 mutations), these genetic aberrations determine around 5% of all breast cancer cases,Template:Cite needed suggesting that the remainder is sporadic. Recently it was found that newly discovered gene called BARD1 if exists in combination with BRCA2 gene may increase the risk of breast cancer to as much as 80 percent.
Alcohol generally appears to increase the risk of breast cancer in people. The UK's Review of Alcohol: Association with Breast Cancer concludes that "studies confirm previous observations that there appears to be an association between alcohol intake and increased risk of breast cancer in women. On balance, there was a weak association between the amount of alcohol consumed and the relative risk."
The National Institute on Alcohol Abuse and Alcoholism (NIAAA) concludes that "Chronic alcohol consumption has been associated with a small (averaging 10 percent) increase in a woman's risk of breast cancer (Friedenreich et al.; Longnecker; Nasca). According to these studies, the risk appears to increase as the quantity and duration of alcohol consumption increases. Other studies, however, have found no evidence of such a link (Chu et al. ; Schatzkin et al.; Webser et al)."Ref.184.108.40.206
The Committee on Carcinogenicity of Chemicals in Food, Consumer Products Non-Technical Summary concludes, "The new research estimates that a woman drinking an average of two units of alcohol per day has a lifetime risk of developing breast cancer 8% higher than a woman who drinks an average of one unit of alcohol per day. The risk of breast cancer further increases with each additional drink consumed per day. … The research also concludes that approximately 6% (between 3.2% and 8.8%) of breast cancers reported in the UK each year could be prevented if drinking was reduced to a very low level (i.e. less than 1 unit/week)."
It has been reported that "Two drinks daily increase the risk of getting breast cancer by about 25 percent." (NCI) but the evidence is inconsistent. The Framingham study has carefully tracked individuals since the 1940s. Data from that research found that drinking alcohol moderately did not increase breast cancer risk (Wellness Facts). Similarly, research by the Danish National Institute for Public Health found that moderate drinking had virtually no effect on breast cancer risk (Petri et al.).
Breast cancer constitutes about 7.3% of all cancers. One study suggests that women who frequently drink red wine may have an increased risk of developing breast cancer.Ref.Maggiolini M. et al. (2005) J Mol Endocrinol. "The red wine phenolics piceatannol and myricetin act as agonists for estrogen receptor alpha in human breast cancer cells"
"Folate intake counteracts breast cancer risk associated with alcohol consumption"Ref.Mayo Clinic news release June 26 2001 "Folate Intake Counteracts Breast Cancer Risk Associated with Alcohol Consumption" and "women who drink alcohol and have a high folate intake are not at increased risk of cancer."Ref.Boston University "Folate, Alcohol, and Cancer Risk" Those who have a high (200 micrograms or more per day) level of folate (folic acid or Vitamin B9) in their diet are not at increased risk of breast cancer compared to those who abstain from alcohol.Ref."A prospective study of folate intake and the risk of breast cancer" Foods rich in folate include citrus fruits, citrus juices, dark green leafy vegetables (such as spinach), dried beans, and peas. Vitamin B9 can also be taken in a multivitamin pill.
Gaining weight after the menopause can increase a woman's risk. Putting on 9.9kg (22lbs) increased the risk of developing breast cancer by 18%.Ref.BBC report Weight link to breast cancer risk
Researchers at the National Cancer Institute and National Institute of Environmental Health Sciences have concluded a study that suggests that artificial light can be a cause of breast cancer.Ref.The Independent Avoid breast cancer. Sleep in the dark...
Persistently increased blood levels of estrogen are associated with an increased risk of breast cancer, as are increased levels of the androgens androstenedione and testosterone (which can be directly converted by aromatase to the estrogens estrone and estradiol, respectively). Increased blood levels of progesterone are associated with a decreased risk of breast cancer in premenopausal women.Ref. A number of circumstances which increase exposure to endogenous estrogens including not having children, delaying first childbirth, not breastfeeding, early menarche (the first menstrual period) and late menopause are suspected of increasing lifetime risk for developing breast cancer.Ref.American Cancer Society. (2006-10-03). What Are the Risk Factors for Breast Cancer? Retrieved 2006-03-30.
Oral contraceptives may produce a slight increase in breast cancer risk among long-term users, but this appears to be a short-term effect. The largest meta-analysis (1996) of data from 54 studies identified a relative risk (RR) of 1.24 for current users; 10 or more years after stopping, no difference was seen. Further, the cancers diagnosed in women who had ever used hormonal contraceptives were less advanced than those in nonusers, raising the possibility that the small excess among users was due to increased detection. Breast cancer risk associated with hormonal contraceptive use did not appear to vary with family history of breast cancer.Cite error: Closing
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