Breast cancer arises when cells within the breast grow and multiply abnormally. This process can lead to the formation of a lump or mass of extra cells, called a tumor. In many cases the tumors are non-cancerous, or benign. In the case of malignant tumors, the cells continue dividing uncontrollably and have the capacity to invade nearby tissues and potentially spread (metastasize) to distant sites. There is also a form of “noninvasive” breast cancer called ductal carcinoma in situ (DCIS); some DCIS tumors may become invasive.
According to the American Cancer Society, breast cancer is the most commonly diagnosed cancer in the United States among women, detected in more than 192,000 women each year. It is the second leading cause of cancer death among women, claiming more than 40,000 lives. (Although it is much rarer, breast cancer can also occur in men. Learn more about male breast cancer.)
Fortunately, the advent and widespread use of mammography has led to a larger proportion of breast cancers being diagnosed in their earlier, more curable stages. Progress in early detection and treatment has led to a decline in breast cancer death rates since 1990. After continuously increasing for more than two decades, the number of breast cancer cases among women has also decreased — by 2.2 percent per year from 1999 through 2005. Such declines in incidence have been partly attributed to reduced use of certain forms of hormone replacement therapy that have been associated with increased breast cancer risk.
Today women with breast cancer have a variety of treatment options, depending on the stage and biology of their disease. Researchers also continue to learn more about the molecular biology of breast cancer, and are developing therapies that are increasingly targeted to specific subtypes of breast cancer.
Memorial Sloan Kettering experts describe efforts to improve our understanding — and treatment — of breast cancer.
To understand the different types of breast cancer, it is helpful to understand the anatomy of the breast.
The female breast is made up of several types of structures designed to produce and deliver nutrition to an infant. Groups of glands called lobules produce milk, which is carried by a series of hollow tubes, called ducts, out through the nipple.
The entire system of glands and ducts is embedded in fat and supportive tissues, with ligaments stretching from the skin to the chest wall to hold breast tissues in place. Blood vessels provide oxygen to breast tissue and carry away wastes. The pectoralis muscle lies against the chest wall underneath each breast.
Also present in the breast is a branch of the lymphatic system, a network of channels and nodes that drains excess fluids from tissue. Lymph fluid enters the lymph channels and is filtered through lymph nodes, where bacteria and foreign particles are trapped and destroyed by immune cells. The lymph nodes closest to the breast are found under the arm (axillary nodes) and under the breastbone (internal mammary nodes).
The breasts undergo many changes as a woman matures. These changes are regulated by hormones. During the reproductive years, breast tissues consist primarily of glands and swell with fluid on a cyclical basis. When pregnancy occurs, the lobules prepare to produce milk. After menopause, when hormone levels drop, the breasts lose their ability to produce milk, and much of the glandular tissue is replaced by less-dense fatty tissue.
Types of Breast Cancer
Doctors from Memorial Sloan Kettering describe some of the risk factors for breast cancer and how to manage them.
There are four major categories of tumors that can occur in the breast:
Lobular Carcinoma in Situ (LCIS)
Lobular carcinoma in situ (LCIS) occurs when abnormal cells develop in the lobules. LCIS is not a cancer, but rather a marker of an increased risk of developing breast cancer in either breast.
Ductal Carcinoma in Situ (DCIS)
Ductal carcinoma in situ (DCIS) is a preinvasive form of breast cancer in which cancer cells arise in the milk ducts, but have not spread. DCIS can progress over time and break out of the milk ducts to become invasive (infiltrating) breast cancer in some women. Treatment for DCIS may consist of surgery and radiation therapy.
Invasive Cancer (also called Infiltrating Cancer)
Invasive cancer cells spread outside of the structures in which they first arise, moving to surrounding tissues and sometimes into the lymph nodes. The majority of breast cancers begin in the ducts. Some develop in the lobules.
Inflammatory Breast Cancer
Rarely, breast cancers appear as inflammatory changes in the breast that mimic other conditions such as a skin infection. The skin may appear red or discolored, or may take on a “peau d'orange” appearance (skin thickening with tiny dimples like an orange peel). Women who observe these breast changes should see a healthcare provider immediately.