Breast cancer

Breast cancer is a cancer of the glandular breast tissue.

 Worldwide, breast cancer is the fifth most common cause of cancer death (after lung cancer, stomach cancer, liver cancer, and colon cancer). In 2005, breast cancer caused 502,000 deaths (7% of cancer deaths; almost 1% of all deaths) worldwide. Among women worldwide, breast cancer is the most common cancer and the most common cause of cancer death.

 In the United States, breast cancer is the third most common cause of cancer death (after lung cancer and colon cancer). In 2007, breast cancer is expected to cause 40,910 deaths (7% of cancer deaths; almost 2% of all deaths) in the U.S. Among women in the U.S., breast cancer is the most common cancer and the second most common cause of cancer death (after lung cancer). Women in the U.S. have a 1 in 8 lifetime chance of developing invasive breast cancer and a 1 in 33 chance of breast cancer causing their death.

The number of cases has significantly increased since the 1970s, a phenomenon partly blamed on modern lifestyles in the Western world.

History

 Breast cancer may be 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." 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.

Classification

 There are numerous ways breast cancer is classified. Like most cancers, breast cancer can be divided into groups based on the tissue of origin, e.g. epithelial (carcinoma) versus stromal (sarcoma). The vast majority of breast cancers arise from epithelial tissue, i.e. they are carcinomas, which can divided further into subclassifications (e.g. DCIS versus LCIS versus papillary carcinoma).

 Other pathologically based classifications: 

    * Location of the tumour origin - breast duct (i.e. ductal) versus breast lobule (i.e. lobular).

    * Histology - see Histologic types section.

    * Grade of tumour - well-differentiated (looks almost like normal tissue) versus poorly differentiated (does not look like any normal tissue/mass of proliferating cells) versus moderately differentiated (somewhere between poorly differentiated and well-differentiated).

    * Stage of the tumour.

    * Immunohistochemical marker status - (ER positive versus ER negative versus HER2/neu positive versus HER2/neu negative), e.g. triple negative breast cancer which is ER negative, PR negative and HER2/neu negative.

    * TNM classification -

          o Tumour size/invasiveness - presence of invasion (poorer prognosis) versus in situ (better prognosis).

          o Nodal status.

          o Presence/absence of metastases.

Histologic types

 Carcinomas 

in situ 

    * Ductal carcinoma (DCIS) 80%

    * Lobular carcinoma (LCIS) 20% 

Invasive

    * Carcinoma NOS (not otherwise specified)

    * Lobular carcinoma

    * Tubular/cribriform carcinoma

    * Mucinous (colloid) carcinoma

    * Medullary carcinoma

    * Papillary carcinoma

    * Metaplastic carcinoma

Sarcomas

     * Phyllodes tumour

 Clinical categorizations

 Breast cancer is occasionally classified clinically (on physical exam findings, (medical) history). Inflammatory breast cancer (IBC) is an example of a clinically classified breast cancer and can be any histologic type.

Symptoms 

Early breast cancer can in some cases present as breast pain (mastodynia) or a painful lump. Since the advent of breast mammography, breast cancer is most frequently discovered as an asymptomatic nodule on a mammogram, before any symptoms are present. A lump under the arm or above the collarbone that does not go away may be present. When breast cancer associates with skin inflammation, this is known as inflammatory breast cancer. In inflammatory breast cancer, the breast tumor itself is causing an inflammatory reaction of the skin, and this can cause pain, swelling, warmth, and redness throughout the breast.

 Changes in the appearance or shape of the breast can raise suspicions of breast cancer.

 Another reported symptom complex of breast cancer is Paget's disease of the breast. This syndrome presents as eczematoid skin changes at the nipple, and is a late manifestation of an underlying breast cancer.

 Most breast symptoms do not turn out to represent underlying breast cancer. Benign breast diseases such as fibrocystic mastopathy, mastitis, functional mastodynia, and fibroadenoma of the breast are more common causes of breast symptoms. The appearance of a new breast symptom should be taken seriously by both patients and their doctors, because of the possibility of an underlying breast cancer at almost any age.

 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. More common sites of metastasis include bone, liver, lung, and brain. 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. Pleural effusions are not uncommon with metastatic breast cancer. Obviously, these symptoms are "non-specific," meaning they can also be manifestations of many other illnesses. 

Epidemiologic risk factors and etiology

Epidemiological