Online Medicine Resource: BREAST CANCER

What is breast cancer?

Breast cancer is a malignancy of the breast, usually involving the ductal or lobular tissues (the tissues involved in milk production). A small percentage of breast cancers tend to cluster in families. These cancers can be caused by mutations in particular genes, such as BRCA1 or BRCA2. In some cases, genetic syndromes involving other cancers also include an increased risk of breast cancer.

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 also be caused by conditions other than breast cancer.

Breast cancers caused by inherited gene mutations tend to occur earlier in life than sporadic (noninherited) cases and are more likely to involve both breasts.

How common is breast cancer?

Each year, more than 215,000 cases of invasive breast cancer are diagnosed in women in the United States. Most breast cancers occur in women, but they can also develop in men (although this is rare). More than 1,400 cases of male breast cancer are diagnosed each year.

An estimated 5 to 10 percent of all breast cancers are hereditary (caused by inherited gene mutations). In the general population, 1 in 500 to 1,000 people have a mutation in the BRCA1 gene that increases their risk of developing cancer. The prevalence of BRCA2 mutations that increase a person's risk is unknown.

What genes are related to breast cancer?

Variations of the ATM, BRCA1, BRCA2, CHEK2, and RAD51 genes increase the risk of developing breast cancer.

The AR, DIRAS3, and ERBB2 genes are associated with breast cancer.

BRCA1 and BRCA2 are the most common genes related to hereditary breast cancer. People with certain mutations in these genes have a high risk of developing breast cancer and several other types of cancer over their lifetimes.

In addition to breast cancer, BRCA1 mutations increase the risk of developing ovarian, prostate, and colon cancers. Men with an inherited mutation in the BRCA2 gene are at an increased risk of breast cancer. In addition, people with BRCA2 mutations have an increased chance of developing cancers of the pancreas, gallbladder, bile duct, and stomach. Melanoma and lymphoma are also more common among people who have BRCA2 mutations.

Other genes such as RAD51, DIRAS3 , ERBB2, and CHEK2 may be involved in the development of breast cancer. Research suggests that some versions of the AR gene may also be associated with breast cancer, although several studies have not shown this connection. People who carry one mutated copy of a gene called ATM have an increased chance of developing several types cancer, including breast cancer, during their lives.

Additional genes are likely associated with breast cancer risk. Many of these genes have not yet been identified or characterised, however.

How do people inherit breast cancer?

The way that breast cancer risk is inherited depends on the gene involved. Mutations in BRCA1 and BRCA2 are inherited in an autosomal dominant pattern, which means only one inherited copy of the altered gene is necessary to increase cancer risk. 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.

Specific mutations in BRCA1 and BRCA2 are more common among certain geographic or ethnic groups. For example, two BRCA1 mutations and one BRCA2 mutation are most common among people of Ashkenazi (central or eastern European) Jewish heritage. Other mutations are more common among people of Norwegian, Icelandic, and Dutch ancestry.