Breast cancer

Breast cancer is a disease in which certain cells in the breast become abnormal and multiply without control or order to form a tumor. The most common form of breast cancer begins in cells lining the ducts that carry milk to the nipple (ductal cancer). Other forms of breast cancer begin in the glands that produce milk (lobular cancer) or in other parts of the breast.

Early breast cancer usually does not cause pain and may exhibit no noticeable symptoms. As the cancer progresses, signs and symptoms can include a lump or thickening in or near the breast; a change in the size or shape of the breast; nipple discharge, tenderness, or retraction (turning inward); and skin irritation, dimpling, or scaliness. These changes can occur as part of many different conditions, however. Having one or more of these symptoms does not mean that a person definitely has breast cancer.

In some cases, cancerous tumors can invade surrounding tissue and spread to other parts of the body. If breast cancer spreads, cancerous cells most often appear in the bones, liver, lungs, or brain. Tumors that begin at one site and then spread to other areas of the body are called metastatic cancers.

A small percentage of all breast cancers cluster in families. Hereditary cancers are those associated with inherited gene mutations. Hereditary breast cancers tend to occur earlier in life than noninherited (sporadic) cases and are more likely to involve both breasts.

Researchers estimate that more than 178,000 new cases of invasive breast cancer will be diagnosed in U.S. women in 2007. Most breast cancers occur in women, but they can also develop in men. Scientists estimate that more than 2,000 new cases of breast cancer will be diagnosed in men in 2007.

An estimated 5 percent to 10 percent of all breast cancers are hereditary. Particular mutations in genes associated with breast cancer are more common among certain geographic or ethnic groups, such as people of Ashkenazi (central or eastern European) Jewish heritage and people of Norwegian, Icelandic, or Dutch ancestry. Particular genetic changes occur more frequently in these groups because they have a shared ancestry over many generations.

Variations of the BRCA1, BRCA2, CDH1, PTEN, STK11, and TP53 genes increase the risk of developing breast cancer.

The AR, ATM, BARD1, BRIP1, CHEK2, DIRAS3, ERBB2, NBN, PALB2, RAD50, and RAD51 genes are associated with breast cancer.

Cancers occur when a buildup of genetic mutations in critical genes—those that control cell growth and division or the repair of damaged DNA—allow cells to grow and divide uncontrollably to form a tumor. In most cases, these genetic changes are acquired during a person's lifetime and are present only in certain cells. These changes, which are called somatic mutations, are not inherited. Less commonly, gene mutations inherited from a parent increase the risk of developing cancer. In people with these inherited genetic changes, additional somatic mutations in other genes must occur for cancer to develop.

In addition to specific genetic changes, researchers have identified many personal and environmental factors that may influence a person's risk of developing breast cancer. These factors include gender, age, ethnic background, a history of previous breast cancer, certain changes in breast tissue, and hormonal factors. A history of breast cancer in closely related family members is also an important risk factor, particularly if the cancer occurred at an early age. Some breast cancers that cluster in families are associated with inherited mutations in particular genes, such as BRCA1 or BRCA2.

BRCA1 and BRCA2 are major genes related to hereditary breast cancer. Women who have inherited certain mutations in these genes have a high risk of developing breast cancer, ovarian cancer, and several other types of cancer during their lifetimes. Men with BRCA1 mutations also have an increased risk of developing breast cancer. Additionally, BRCA1 mutations are associated with an increased risk of pancreatic cancer. Mutations in the BRCA2 gene are associated with an increased chance of developing male breast cancer and cancers of the prostate and pancreas. An aggressive form of skin cancer called melanoma is also more common among people who have BRCA2 mutations.

Inherited changes in several other genes, including CDH1, PTEN, STK11, and TP53, have been found to increase the risk of developing breast cancer. Mutations in these genes cause syndromes that greatly increase the chance of developing several types of cancer over a person's lifetime. Some of these syndromes also include other signs and symptoms, such as the growth of noncancerous (benign) tumors.

Some research suggests that inherited variants of the ATM, BARD1, BRIP1, CHEK2, NBN, PALB2, RAD50, and RAD51 genes, as well as certain versions of the AR gene, may also be associated with breast cancer risk. Not all studies have shown these connections, however. Of these genes, ATM and CHEK2 have the strongest evidence of being related to the risk of developing breast cancer.

Noninherited (somatic) mutations also have been identified in breast tumors. For example, somatic mutations in the ERBB2 (also called Her-2/neu), DIRAS3, and TP53 genes have been associated with some cases of breast cancer.

Most cases of breast cancer are not inherited. These cancers are associated with genetic changes that occur only in breast cancer cells (somatic mutations) and occur during a person's lifetime.

In hereditary breast cancer, the way that cancer risk is inherited depends on the gene involved. For example, mutations in the BRCA1 and BRCA2 genes are inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to increase a person's chance of developing cancer. In other cases, the inheritance of breast cancer risk is unclear. It is important to note that people inherit an increased risk of cancer, not the disease itself. Not all people who inherit mutations in these genes will develop cancer.