Breast cancer is a disease in which certain cells in the breast become abnormal and multiply uncontrollably to form a tumor. Although breast cancer is much more common in women, this form of cancer can also develop in men. In both women and men, the most common form of breast cancer begins in cells lining the milk ducts (ductal cancer). In women, cancer can also develop in the glands that produce milk (lobular cancer). Most men have little or no lobular tissue, so lobular cancer in men is very rare.

In its early stages, 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. However, these changes can occur as part of many different conditions. 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. These cancers are described as hereditary and are associated with inherited gene mutations. Hereditary breast cancers tend to develop earlier in life than non-inherited (sporadic) cases, and new (primary) tumors are more likely to develop in both breasts

Breast cancer is the second most commonly diagnosed cancer in women. (Only skin cancer is more common.) About one in eight women in the United States will develop invasive breast cancer in her lifetime. Male breast cancer represents less than 1 percent of all breast cancer diagnoses. Particular gene mutations associated with breast cancer are more common among certain geographic or ethnic groups.

Cancers occur when a buildup of mutations in critical genes—those that control cell growth and division or repair damaged DNA—allow cells to grow and divide uncontrollably to form a tumor In most cases of breast cancer, these genetic changes are acquired during a person’s lifetime and are present only in certain cells in the breast. These changes, which are called somatic mutations, are not inherited. Somatic mutations in many different genes have been found in breast cancer cells. Less commonly, gene mutations present in essentially all of the body’s cells increase the risk of developing breast cancer. These genetic changes, which are classified as germline mutations, are usually inherited from a parent. In people with germline mutations, changes in other genes, together with environmental and lifestyle factors, also influence whether a person will develop breast cancer.

Breast cancer is the most common cancer in women. One in eight women will develop breast cancer in their lifetime. Breast cancer occurs when the cells in the breast begin to grow abnormally into a malignant tumor. About 5-10% of cases are inherited (hereditary breast cancer), while most are not. Hereditary breast cancer (HBC) occurs when a person has a genetic change (mutation) that causes their cells to be more likely to become cancerous. The mutation can be passed through generations in a family. Women and men with HBC have a higher risk of developing breast, and sometimes other cancers or health problems, as well.

 Hereditary breast cancer syndromes are conditions that impact other areas of an individual’s body in addition to increasing their risk for breast cancer. A syndrome can be inherited in a dominant, de novo, or recessive manner. Some examples of hereditary breast cancer syndromes are listed below. 2/3 Cowden syndrome (CS) People with Cowden syndrome often have large heads (macrocephaly) and are at an increased risk for different types of benign and malignant tumors, including endometrial, thyroid, and breast cancer. CS is caused by a mutation in the PTEN gene. The lifetime risk for breast cancer in women with Cowden syndrome can be as high as 85%. Ataxia telangiectasia (AT) Ataxia telangiectasia is a condition that usually presents in childhood with movement difficulties and frequent infections, in addition to a higher risk for cancer. AT is caused by a mutation in the ATM gene. Fanconi anemia (FA) Fanconi anemia can be caused by having two mutations in a number of different genes, and can lead to physical anomalies and progressive bone marrow failure. An increased risk of breast cancer is seem in some individuals with one mutation in a FA-associated gene.