Breast cancer is the second-most-common cancer, and the second-leading cause of cancer deaths, among women. Most breast cancers are slow-growing, but there are types that are aggressive, which is why early detection is essential. Breast cancer is defined by the type of breast cells in which it begins, and is generally categorized as invasive or noninvasive. Breast cancer can also affect men, but it is 100 times more common in women.
Types of Breast Cancer
Two types of cancer that occur rarely are inflammatory breast disease, in which cancerous cells block the lymph vessels within the breast, and Paget disease of the nipple, in which the cells in or around the nipple become cancerous. They account for, respectively, approximately one to six percent, and approximately one percent, of breast cancers. The two most common types of breast cancer are ductal carcinoma and lobular carcinoma.
This is the most prevalent type of breast cancer, and it begins in the cells that line the milk ducts. More than half of breast cancer cases diagnosed each year are of this type. There are two kinds of ductal carcinoma.
Ductal carcinoma in situ (DCIS)
With DCIS, cancer cells are found only in the milk-duct lining, and have not spread to other breast tissue. DCIS is often discovered when a mammogram is done as part of a regular screening. In recent years, the number of DCIS diagnoses has increased dramatically, primarily because the number of screening mammograms has increased. DCIS is not life-threatening, but requires treatment to make sure the cancer does not spread.
Invasive ductal carcinoma (IDC)
With IDC, cancer cells have spread from the ducts to other parts of breast tissue. This is the most common type of invasive breast cancer, requiring treatment at an early stage to make sure it does not spread from breast tissue to other parts of the body. It accounts for approximately 65 to 85 percent of invasive-type breast cancer cases.
Lobular carcinoma begins in the breast's milk-producing glands, which are called lobules. The breast contains 15 to 20 lobes; the lobules are the smaller lobes within them. There are two types of lobular carcinoma:
Lobular carcinoma in situ (LCIS)
With LCIS, abnormal (rather than cancerous) cells are found only in the breast lobules; they do not spread to other tissue. LCIS is asymptomatic, and usually does not show up on mammograms. It is often discovered when a biopsy is performed for another reason.
Invasive lobular carcinoma (ILC)
With ILC, cancer cells spread from the lobules to close-by breast tissue. It requires treatment at an early stage to make sure it does not spread from the breast to other parts of the body. It accounts for approximately 10 to 15 percent of invasive-type breast cancer cases.
Risk Factors for Breast Cancer
The greatest risk factor for developing breast cancer is being female, probably because men produce much less estrogen and progesterone, hormones that can promote the growth of malignant breast cells. Other risk factors for women include the following: