What is Breast Cancer?

Breast cancer is an uncontrolled growth of breast cells. To better understand breast cancer, it helps to understand how any cancer can develop.
Cancer occurs as a result of mutations, or abnormal changes, in the genes responsible for regulating the growth of cells and keeping them healthy. The genes are in each cell’s nucleus, which acts as the “control room” of each cell. Normally, the cells in our bodies replace themselves through an orderly process of cell growth: healthy new cells take over as old ones die out. But over time, mutations can “turn on” certain genes and “turn off” others in a cell. That changed cell gains the ability to keep dividing without control or order, producing more cells just like it and forming a tumor.
A tumor can be benign (not dangerous to health) or malignant (has the potential to be dangerous). Benign tumors are not considered cancerous: their cells are close to normal in appearance, they grow slowly, and they do not invade nearby tissues or spread to other parts of the body. Malignant tumors are cancerous. Left unchecked, malignant cells eventually can spread beyond the original tumor to other parts of the body.
The term “breast cancer” refers to a malignant tumor that has developed from cells in the breast. Usually breast cancer either begins in the cells of the lobules, which are the milk-producing glands, or the ducts, the passages that drain milk from the lobules to the nipple. Less commonly, breast cancer can begin in the stromal tissues, which include the fatty and fibrous connective tissues of the breast.

Breast Anatomy

• Larger Version

Over time, cancer cells can invade nearby healthy breast tissue and make their way into the underarm lymph nodes, small organs that filter out foreign substances in the body. If cancer cells get into the lymph nodes, they then have a pathway into other parts of the body. The breast cancer’s stage refers to how far the cancer cells have spread beyond the original tumor (see Stages of Breast Cancer table for more information).
Breast cancer is always caused by a genetic abnormality (a “mistake” in the genetic material). However, only 5-10% of cancers are due to an abnormality inherited from your mother or father. About 90% of breast cancers are due to genetic abnormalities that happen as a result of the aging process and the “wear and tear” of life in general.
There are steps every person can take to help the body stay as healthy as possible and lower risk of breast cancer or a breast cancer recurrence (such as maintaining a healthy weight, not smoking, limiting alcohol, and exercising regularly). Learn what you can do to manage breast cancer risk factors. Always remember, breast cancer is never anyone's fault. Feeling guilty, or telling yourself that breast cancer happened because of something you or anyone else did, is not productive.

Stages of Breast Cancer

Stage	Definition
Stage 0	Cancer cells remain inside the breast duct, without invasion into normal adjacent breast tissue.
Stage IA	The tumor measures up to 2 cm AND the cancer has not spread outside the breast; no lymph nodes are involved
Stage IB	There is no tumor in the breast; instead, small groups of cancer cells -- larger than 0.2 millimeter but not larger than 2 millimeters – are found in the lymph nodes OR there is a tumor in the breast that is no larger than 2 centimeters, and there are small groups of cancer cells – larger than 0.2 millimeter but not larger than 2 millimeters – in the lymph nodes.
Stage IIA	No tumor can be found in the breast, but cancer cells are found in the axillary lymph nodes (the lymph nodes under the arm) OR the tumor measures 2 centimeters or smaller and has spread to the axillary lymph nodes OR the tumor is larger than 2 but no larger than 5 centimeters and has not spread to the axillary lymph nodes.
Stage IIB	The tumor is larger than 2 but no larger than 5 centimeters and has spread to the axillary lymph nodes OR the tumor is larger than 5 centimeters but has not spread to the axillary lymph nodes.
Stage IIIA	No tumor is found in the breast. Cancer is found in axillary lymph nodes that are sticking together or to other structures, or cancer may be found in lymph nodes near the breastbone OR the tumor is any size. Cancer has spread to the axillary lymph nodes, which are sticking together or to other structures, or cancer may be found in lymph nodes near the breastbone.
Stage IIIB	The tumor may be any size and has spread to the chest wall and/or skin of the breast AND may have spread to axillary lymph nodes that are clumped together or sticking to other structures, or cancer may have spread to lymph nodes near the breastbone. Inflammatory breast cancer is considered at least stage IIIB.
Stage IIIC	There may either be no sign of cancer in the breast or a tumor may be any size and may have spread to the chest wall and/or the skin of the breast AND the cancer has spread to lymph nodes either above or below the collarbone AND the cancer may have spread to axillary lymph nodes or to lymph nodes near the breastbone.
Stage IV	The cancer has spread — or metastasized — to other parts of the body.

WHAT WIKIPEDIA SAYS ABOUT BREAST CANCER

Breast cancer is a type of cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk.^[1] Cancers originating from ducts are known as ductal carcinomas, while those originating from lobules are known as lobular carcinomas. Breast cancer occurs in humans and other mammals. While the overwhelming majority of human cases occur in women, male breast cancer can also occur.^[2]
The size, stage, rate of growth, and other characteristics of a breast cancer determine the kinds of treatment. Treatment may include surgery, drugs (hormonal therapy and chemotherapy), radiation and/or immunotherapy.^[3] Surgical removal of the tumor provides the single largest benefit, with surgery alone curing many cases. To increase the likelihood of cure, several chemotherapy regimens are commonly given in addition to surgery. Radiation is used after breast-conserving surgery and substantially improves local relapse rates and in many circumstances also overall survival.^[4] Some breast cancers are sensitive to hormones such as estrogen and/or progesterone, which makes it possible to treat them by blocking the effects of these hormones.
Worldwide, breast cancer comprises 22.9% of all cancers (excluding non-melanoma skin cancers) in women.^[5] In 2008, breast cancer caused 458,503 deaths worldwide (13.7% of cancer deaths in women).^[5] Breast cancer is more than 100 times more common in women than in men, although men tend to have poorer outcomes due to delays in diagnosis.^[6][7]
Prognosis and survival rates for breast cancer vary greatly depending on the cancer type, stage, treatment, and geographical location of the patient. Survival rates in the Western world are high;^[6] for example, more than 8 out of 10 women (84%) in England diagnosed with breast cancer survive for at least 5 years.^[8] In developing countries, however, survival rates are much poorer.

Signs and symptoms

Early signs of breast cancer

Breast cancer showing an inverted nipple, lump and skin dimpling.

The first noticeable symptom of breast cancer is typically a lump that feels different from the rest of the breast tissue. More than 80% of breast cancer cases are discovered when the woman feels a lump.^[9] The earliest breast cancers are detected by a mammogram.^[10] Lumps found in lymph nodes located in the armpits^[9] can also indicate breast cancer.
Indications of breast cancer other than a lump may include thickening different from the other breast tissue, one breast becoming larger or lower, a nipple changing position or shape or becoming inverted, skin puckering or dimpling, a rash on or around a nipple, discharge from nipple/s, constant pain in part of the breast or armpit, and swelling beneath the armpit or around the collarbone.^[11] Pain ("mastodynia") is an unreliable tool in determining the presence or absence of breast cancer, but may be indicative of other breast health issues.^[9][10][12]
Inflammatory breast cancer is a particular type of breast cancer which can pose a substantial diagnostic challenge. Symptoms may resemble a breast inflammation and may include itching, pain, swelling, nipple inversion, warmth and redness throughout the breast, as well as an orange-peel texture to the skin referred to as peau d'orange;^[9] the absence of a discernible lump delays detection dangerously.
Another reported symptom complex of breast cancer is Paget's disease of the breast. This syndrome presents as eczematoid skin changes such as redness and mild flaking of the nipple skin. As Paget's advances, symptoms may include tingling, itching, increased sensitivity, burning, and pain. There may also be discharge from the nipple. Approximately half of women diagnosed with Paget's also have a lump in the breast.^[13]
In rare cases, what initially appears as a fibroadenoma (hard movable lump) could in fact be a phyllodes tumor. Phyllodes tumors are formed within the stroma (connective tissue) of the breast and contain glandular as well as stromal tissue. Phyllodes tumors are not staged in the usual sense; they are classified on the basis of their appearance under the microscope as benign, borderline, or malignant.^[14]
Occasionally, breast cancer presents as metastatic disease, that is, cancer that has spread beyond the original organ. Metastatic breast cancer will cause symptoms that depend on the location of metastasis. Common sites of metastasis include bone, liver, lung and brain.^[15] Unexplained weight loss can occasionally herald an occult breast cancer, as can symptoms of fevers or chills. Bone or joint pains can sometimes be manifestations of metastatic breast cancer, as can jaundice or neurological symptoms. These symptoms are called non-specific, meaning they could be manifestations of many other illnesses.^[16]
Most symptoms of breast disorders, including most lumps, do not turn out to represent underlying breast cancer. Less than 20% of lumps for example are cancer^[17] and benign breast diseases such as mastitis and fibroadenoma of the breast are more common causes of breast disorder symptoms. Nevertheless, the appearance of a new symptom should be taken seriously by both patients and their doctors, because of the possibility of an underlying breast cancer at almost any age.^[18]

Risk factors

Main article: Risk factors of breast cancer

The primary risk factors for breast cancer are female sex and older age.^[19] Other potential risk factors include: lack of childbearing or breastfeeding,^[20] higher hormone levels,^[21][22] diet and obesity.

Lifestyle

See also: List of breast carcinogenic substances

Smoking tobacco appears to increase the risk of breast cancer with the greater the amount of smoked and the earlier in life smoking began the higher the risk.^[23] In those who are long term smokers the risk is increased 35% to 50%.^[23] A lack of physical activity has been linked to ~10% of cases.^[24]
The association between breast feeding and breast cancer has not been clearly determined with some studies finding support for an association and others not.^[25] In the 1980s the abortion–breast cancer hypothesis posited that induced abortion increased the risk of developing breast cancer.^[26] This hypothesis has been the subject of extensive scientific inquiry which has concluded that neither miscarriages nor abortions are associated.^[27] There may be an association between oral contraceptives and the development of premenopausal breast cancer.^[28] Whether or not this association is causal is debated and if there is indeed a link the absolute effect is small.^[29][30] In those with BRCA1 or BRCA2 mutations or a family history modern OCPs do not appear to affect the subsequent risk of breast cancer.^[31][32]
There is a relationship between diet and breast cancer including an increased risk with a high fat diet,^[33] alcohol intake,^[34] and obesity.^[35] Dietary iodine deficiency may also play a role.^[36]
Other risk factors include radiation,^[37] and shift-work.^[38] A number of chemicals have also been linked including: polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and organic solvents.^[39] Although the radiation from mammography is a low dose, it is estimated that yearly screening from 40 to 80 years of age will cause ~225 cases of fatal breast cancer per million women screened.^[40]

[edit] Genetics

Some genetic susceptibility probably plays a role in most cases.^[41] Overall however genetics is believed to be the cause of 5-10% of all cases.^[42] In those with zero, one or two affected relatives the risk of breast cancer before the age of 80 is 7.8%, 13.3%, and 21.1% with a subsequent mortality from the disease of 2.3%, 4.2%, and 7.6% respectively.^[43] In those with a first degree relative with the disease the risk of breast cancer between the age of 40 and 50 is double that of the general population.^[44]
In less than 5% of cases genetics plays a more significant role.^[41] This include those who carry the BRCA1 and BRCA2 gene mutation.^[41] These mutations account for up to 90% of the total genetic influence with a risk of breast cancer of 60-80% in those affected.^[42] Other significant mutations include: p53 (Li-Fraumeni syndrome), PTEN (Cowden syndrome), and STK11 (Peutz–Jeghers syndrome), CHEK2, ATM, BRIP1, and PALB2.^[42]

[edit] Medical conditions

Certain breast changes: atypical hyperplasia and lobular carcinoma in situ found in benign breast conditions such as fibrocystic breast changes are correlated with an increased breast cancer risk.^{[citation needed]}

[edit] Pathophysiology

Main article: Carcinogenesis

Overview of signal transduction pathways involved in apoptosis. Mutations leading to loss of apoptosis can lead to tumorigenesis.

Breast cancer, like other cancers, occurs because of an interaction between the environment and a defective gene. Normal cells divide as many times as needed and stop. They attach to other cells and stay in place in tissues. Cells become cancerous when mutations destroy their ability to stop dividing, to attach to other cells and to stay where they belong.
Normal cells will commit cell suicide (apoptosis) when they are no longer needed. Until then, they are protected from cell suicide by several protein clusters and pathways. One of the protective pathways is the PI3K/AKT pathway; another is the RAS/MEK/ERK pathway. Sometimes the genes along these protective pathways are mutated in a way that turns them permanently "on", rendering the cell incapable of committing suicide when it is no longer needed. This is one of the steps that causes cancer in combination with other mutations. Normally, the PTEN protein turns off the PI3K/AKT pathway when the cell is ready for cell suicide. In some breast cancers, the gene for the PTEN protein is mutated, so the PI3K/AKT pathway is stuck in the "on" position, and the cancer cell does not commit suicide.^[45]
Mutations that can lead to breast cancer have been experimentally linked to estrogen exposure.^[46]
Failure of immune surveillance, the removal of malignant cells throughout one's life by the immune system.^[47] Abnormal growth factor signaling in the interaction between stromal cells and epithelial cells can facilitate malignant cell growth.^[48][49] In breast adipose tissue, overexpression of leptin leads to increased cell proliferation and cancer.^[50]
In the United States, 10 to 20 percent of patients with breast cancer and patients with ovarian cancer have a first- or second-degree relative with one of these diseases. The familial tendency to develop these cancers is called hereditary breast—ovarian cancer syndrome. The best known of these, the BRCA mutations, confer a lifetime risk of breast cancer of between 60 and 85 percent and a lifetime risk of ovarian cancer of between 15 and 40 percent. Some mutations associated with cancer, such as p53, BRCA1 and BRCA2, occur in mechanisms to correct errors in DNA. These mutations are either inherited or acquired after birth. Presumably, they allow further mutations, which allow uncontrolled division, lack of attachment, and metastasis to distant organs.^[37][51]However there is strong evidence of residual risk variation that goes well beyond hereditary BRCA gene mutations between carrier families. This is caused by unobserved risk factors.^[52] This implicates environmental and other causes as triggers for breast cancers. The inherited mutation in BRCA1 or BRCA2 genes can interfere with repair of DNA cross links and DNA double strand breaks (known functions of the encoded protein)^[53] These carcinogens cause DNA damage such as DNA cross links and double strand breaks that often require repairs by pathways containing BRCA1 and BRCA2.^[54][55] However, mutations in BRCA genes account for only 2 to 3 percent of all breast cancers.^[56] About half of hereditary breast–ovarian cancer syndromes involve unknown genes.

[edit] Diagnosis

Most types of breast cancer are easy to diagnose by microscopic analysis of the biopsy. There are however, rarer types of breast cancer that require specialized lab exams.
While screening techniques are useful in determining the possibility of cancer, a further testing is necessary to confirm whether a lump detected on screening is cancer, as opposed to a benign alternative such as a simple cyst.
Very often the results of noninvasive examination, mammography and additional tests that are performed in special circumstances such as ultrasound or MR imaging are sufficient to warrant excisional biopsy as the definitive diagnostic and curative method.
Both mammography and clinical breast exam, also used for screening, can indicate an approximate likelihood that a lump is cancer, and may also detect some other lesions.^[57] When the tests are inconclusive Fine Needle Aspiration and Cytology (FNAC) may be used. FNAC may be done in a GP's office using local anaesthetic if required, involves attempting to extract a small portion of fluid from the lump. Clear fluid makes the lump highly unlikely to be cancerous, but bloody fluid may be sent off for inspection under a microscope for cancerous cells. Together, these three tools can be used to diagnose breast cancer with a good degree of accuracy.
Other options for biopsy include core biopsy, where a section of the breast lump is removed, and an excisional biopsy, where the entire lump is removed.
In addition vacuum-assisted breast biopsy (VAB) may help diagnose breast cancer among patients with a mammographically detected breast in women.^[58]

• 

  Excised human breast tissue, showing an irregular, dense, white stellate area of cancer 2 cm in diameter, within yellow fatty tissue.

[edit] Classification

Main article: Breast cancer classification

Breast cancers are classified by several grading systems. Each of these influences the prognosis and can affect treatment response. Description of a breast cancer optimally includes all of these factors.

• Histopathology. Breast cancer is usually classified primarily by its histological appearance. Most breast cancers are derived from the epithelium lining the ducts or lobules, and these cancers are classified as ductal or lobular carcinoma. Carcinoma in situ is growth of low grade cancerous or precancerous cells within a particular tissue compartment such as the mammary duct without invasion of the surrounding tissue. In contrast, invasive carcinoma does not confine itself to the initial tissue compartment.^[59]

• Grade. Grading compares the appearance of the breast cancer cells to the appearance of normal breast tissue. Normal cells in an organ like the breast become differentiated, meaning that they take on specific shapes and forms that reflect their function as part of that organ. Cancerous cells lose that differentiation. In cancer, the cells that would normally line up in an orderly way to make up the milk ducts become disorganized. Cell division becomes uncontrolled. Cell nuclei become less uniform. Pathologists describe cells as well differentiated (low grade), moderately differentiated (intermediate grade), and poorly differentiated (high grade) as the cells progressively lose the features seen in normal breast cells. Poorly differentiated cancers have a worse prognosis.

• Stage. Breast cancer staging using the TNM system is based on the size of thetumor (T), whether or not the tumor has spread to the lymph nodes (N) in the armpits, and whether the tumor has metastasized (M) (i.e. spread to a more distant part of the body). Larger size, nodal spread, and metastasis have a larger stage number and a worse prognosis.
  The main stages are:
  • Stage 0 is a pre-cancerous or marker condition, either ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS).
  • Stages 1–3 are within the breast or regional lymph nodes.
  • Stage 4 is 'metastatic' cancer that has a less favorable prognosis.

• Receptor status. Breast cancer cells have receptors on their surface and in their cytoplasm and nucleus. Chemical messengers such as hormones bind to receptors, and this causes changes in the cell. Breast cancer cells may or may not have three important receptors: estrogen receptor (ER), progesterone receptor (PR), and HER2.
  ER+ cancer cells depend on estrogen for their growth, so they can be treated with drugs to block estrogen effects (e.g. tamoxifen), and generally have a better prognosis. HER2+ breast cancer had a worse prognosis,^[60] but HER2+ cancer cells respond to drugs such as the monoclonal antibody trastuzumab (in combination with conventional chemotherapy), and this has improved the prognosis significantly.^[61] Cells with none of these receptors are called triple negative although they frequently express receptors for other hormones such as androgen receptor and prolactin receptor.

• DNA assays. DNA testing of various types including DNA microarrays have compared normal cells to breast cancer cells. The specific changes in a particular breast cancer can be used to classify the cancer in several ways, and may assist in choosing the most effective treatment for that DNA type.

[edit] Prevention

The World Cancer Research Fund indicated that women can reduce their risk of breast cancer by maintaining a healthy weight, drinking less alcohol, being physically active and breastfeeding their children.^[62] These modifications might prevent 38% of breast cancers in the US, 42% in the UK, 28% in Brazil and 20% in China.^[62] The benefits with moderate exercise such as brisk walking are seen at all age groups including postmenopausal women.^[62][63]
Prophylactic bilateral mastectomy may be considered in people with BRCA1 and BRCA2 mutations.^[64][65] Some carcinogens are known to take advantage of deficiencies in processes that depend on normal BRCA1 and BRCA2 function.

[edit] Screening

Main article: Breast cancer screening

Breast cancer screening refers to testing otherwise-healthy women for breast cancer in an attempt to achieve an earlier diagnosis. The assumption is that early detection will improve outcomes. A number of screening test have been employed including: clinical and self breast exams, mammography, genetic screening, ultrasound, and magnetic resonance imaging.
A clinical or self breast exam involves feeling the breast for lumps or other abnormalities. Research evidence does not support the effectiveness of either type of breast exam, because by the time a lump is large enough to be found it is likely to have been growing for several years and will soon be large enough to be found without an exam.^[66] Mammographic screening for breast cancer uses x-rays to examine the breast for any uncharacteristic masses or lumps.
For the average woman, the U.S. Preventive Services Task Force recommends (2009) mammography every two years in women between the ages of 50 and 74.^[67] The European Cancer Observatory (2011) recommends mammography every 2 - 3 years between 50 and 69.^[68] These task force reports point out that in addition to unnecessary surgery and anxiety, the risks of more frequent mammograms include a small but significant increase in breast cancer induced by radiation.^[69] More recently, the Cochrane Collaboration (2011) concluded that mammograms reduce mortality from breast cancer by 15% or .05% absolute, but also result in unnecessary surgery and anxiety, resulting in their view that it is not clear whether mammography screening does more good or harm.^[70] The US Cochrane Collaboration now refer readers to The Nordic Cochrane Collection (2012), which reviews updated research to state that advances in diagnosis and treatment make mammography screening less effective today. They state screening is “no longer effective.” They conclude that “it therefore no longer seems reasonable to attend” for breast cancer screening at any age, and warn of misleading information on the internet.^[71]
Molecular breast imaging is currently under study and may also be an alternative.^[72]

[edit] Management

Main article: Breast cancer treatment

Breast cancer is usually treated with surgery and then possibly with chemotherapy or radiation, or both. A multidisciplinary approach is preferable.^[73] Hormone positive cancers are treated with long term hormone blocking therapy. Treatments are given with increasing aggressiveness according to the prognosis and risk of recurrence. The NPI Nottingham Prognostic Index is a useful tool in assessing the prognosis

• Stage 1 cancers (and DCIS) have an excellent prognosis and are generally treated with lumpectomy and sometimes radiation.^[74] HER2+ cancers should be treated with the trastuzumab (Herceptin) regime.^[75] Chemotherapy is uncommon for other types of stage 1 cancers.
• Stage 2 and 3 cancers with a progressively poorer prognosis and greater risk of recurrence are generally treated with surgery (lumpectomy or mastectomy with or without lymph node removal), chemotherapy (plus trastuzumab for HER2+ cancers) and sometimes radiation (particularly following large cancers, multiple positive nodes or lumpectomy).
• Stage 4, metastatic cancer, (i.e. spread to distant sites) has poor prognosis and is managed by various combination of all treatments from surgery, radiation, chemotherapy and targeted therapies. 10 year survival rate is 5% without treatment and 10% with optimal treatment.^[76]

[edit] Surgery

Chest after right breast mastectomy

Surgery involves the physical removal of the tumor, typically along with some of the surrounding tissue and frequently sentinel node biopsy.
Standard surgeries include:

• Mastectomy: Removal of the whole breast.
• Quadrantectomy: Removal of one quarter of the breast.
• Lumpectomy: Removal of a small part of the breast.

If the patient desires, then breast reconstruction surgery, a type of cosmetic surgery, may be performed to create an aesthetic appearance. In other cases, women use breast prostheses to simulate a breast under clothing, or choose a flat chest.

[edit] Medication

Drugs used after and in addition to surgery are called adjuvant therapy. Chemotherapy or other types of therapy prior to surgery are called neoadjuvant therapy.
There are currently three main groups of medications used for adjuvant breast cancer treatment: hormone blocking therapy, chemotherapy, and monoclonal antibodies.

Hormone blocking therapy

Some breast cancers require estrogen to continue growing. They can be identified by the presence of estrogen receptors (ER+) and progesterone receptors (PR+) on their surface (sometimes referred to together as hormone receptors). These ER+ cancers can be treated with drugs that either block the receptors, e.g. tamoxifen (Nolvadex), or alternatively block the production of estrogen with an aromatase inhibitor, e.g. anastrozole (Arimidex)^[77] or letrozole (Femara). Aromatase inhibitors, however, are only suitable for post-menopausal patients. This is because the active aromatase in postmenopausal women is different from the prevalent form in premenopausal women, and therefore these agents are ineffective in inhibiting the predominant aromatase of premenopausal women.^[78]

Chemotherapy

Predominately used for stage 2–4 disease, being particularly beneficial in estrogen receptor-negative (ER-) disease. They are given in combinations, usually for 3–6 months. One of the most common treatments is cyclophosphamide plus doxorubicin (Adriamycin), known as AC. Most chemotherapy medications work by destroying fast-growing and/or fast-replicating cancer cells either by causing DNA damage upon replication or other mechanisms; these drugs also damage fast-growing normal cells where they cause serious side effects. Damage to the heart muscle is the most dangerous complication of doxorubicin. Sometimes a taxane drug, such as docetaxel, is added, and the regime is then known as CAT; taxane attacks the microtubules in cancer cells. Another common treatment, which produces equivalent results, is cyclophosphamide, methotrexate, and fluorouracil (CMF). (Chemotherapy can literally refer to any drug, but it is usually used to refer to traditional non-hormone treatments for cancer.)^{[citation needed]}

Monoclonal antibodies

Trastuzumab (Herceptin), a monoclonal antibody to HER2, has improved the 5 year disease free survival of stage 1–3 HER2+ breast cancers to about 87% (overall survival 95%).^[79] Trastuzumab, however, is expensive, and approximately 2% of patients suffer significant heart damage.^[80] Other monoclonal antibodies are also undergoing clinical trials. Trastuzumab is only effective in patients with the HER2 mutation.

Between 25 and thirty percent of breast cancers have an amplification of the HER2 gene or overexpression of its protein product.^[81] This receptor is normally stimulated by a growth factor which causes the cell to divide; in the absence of the growth factor, the cell will normally stop growing. Overexpression of this receptor in breast cancer is associated with increased disease recurrence and worse prognosis.
Aspirin may reduce mortality from breast cancer.^[82]

Source: http://en.wikipedia.org/wiki/Breast_cancer




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