Although the majority of breast lumps are benign, nearly one-quarter will be cancerous. But not all breast cancers are the same. Most are carcinomas - that is, cancers that arise from epithelial (surface or lining) tissues - and most develop in the breast lobules (glands that produce milk) or tissues known as terminal ductolobular units (TDLU). Such cancers include ductal carcinomas and lobular carcinomas. Paget's disease (cancer of the areola and nipple) and inflammatory carcinoma (a highly malignant cancer) account for nearly all remaining types of breast cancer.
Often breast tumors are discovered at an early stage, when they are still small and confined. In such cases, cancer cells have not grown into the surrounding tissues and remain within the borders of a duct or lobule. These tumors are known as non-invasive, in situ tumors (tumors that remain 'in the site' of origin).
In situ tumors are too tiny to have formed a 'lump,' and so they usually are not felt or detected during a physical exam. They are diagnosed by mammography (breast x-ray). Non-invasive carcinomas include
- ductal carcinoma in situ (DCIS), and
- lobular carcinoma in situ (LCIS).
Ductal carcinoma in situ (DCIS; also known as intraductal carcinoma or non-invasive ductal carcinoma) contains breast duct cells that have malignant characteristics when viewed under a microscope. Therefore, this
The treatment of DCIS is a topic of great debate. Experts continue to argue about whether to treat DCIS by some form of breast-conserving surgery, with or without radiation, or by mastectomy.
Lobular carcinoma in situ (LCIS; also known as non-invasive lobular carcinoma) usually occurs in women who have not undergone
Paget's disease is a slow-growing cancer of the nipple. It usually strikes middle-aged women and may occur in association with an underlying in situ or invasive ductal carcinoma of the breast. Paget's disease arises in the ducts beneath the nipple and then grows onto the nipple itself. Because the tumor may cause crustiness, oozing, and itching of the areola and nipple, sometimes it is incorrectly diagnosed as eczema or another skin condition. Yet Paget's disease is distinguished by the fact that it does not involve the surrounding skin and typically is limited to one breast.
If breast cancer penetrates the membrane that surrounds the lobules or ducts, it is called an infiltrating or invasive carcinoma. Invasive carcinomas - like ductal carcinoma and lobular carcinoma - can grow into the supporting tissue between the ducts, blood vessels, lymph nodes, and other structures with the breasts. Therefore, there is a greater chance that invasive carcinoma will metastasize, spreading throughout the body.
About 75% percent of all invasive breast cancers are ductal carcinomas. Under the microscope, ductal carcinoma looks like a mass with poorly defined edges that have begun to extend into the surrounding tissue. As the cancer invades the fatty tissue around a duct, it causes the formation of fibrous, scar-like tissue. Such scar formation may make ductal carcinoma appear larger than it actually is. Depending upon the location of the tumor, the symptoms of invasive ductal carcinoma may include retraction (drawing inward) of the nipple or nipple discharge and skin changes such as wrinkling or dimpling.
Lobular carcinomas make up approximately 5% to 10% of all invasive breast cancers. Lobular breast cancer is more difficult to detect by mammography because it may not occur as a distinct lump. Instead, lobular carcinoma may appear as an irregular thickening in the breast. A small proportion of women (~5%) may develop lobular carcinoma in both breasts.
In addition to ductal and lobular carcinoma, three well recognized types of invasive breast cancer are:
- tubular cancers (slow-growing, tube-shaped cancers)
- medullary cancers (cancers that look like the medulla [gray matter] of the brain), and
- mucinous cancers (cancers that contain a mucous protein).
Inflammatory carcinoma is a very serious, rapidly spreading type of tumor that accounts for about 1% of all breast cancers. It produces symptoms like swelling, redness, and skin warmth, which result from blockage of the skin's lymphatic vessels by cancer cells. Because of such symptoms, inflammatory carcinoma sometimes is confused with mastitis - a breast infection that may or may not be associated with breastfeeding and can be cured by antibiotics. In the past, a diagnosis of inflammatory carcinoma was particularly grim, since the majority of people died from the disease within a year. However, new, aggressive forms of
Rare Breast Cancers
Although most breast cancers are carcinomas - tumors that develop from epithelial (surface or lining) tissues - a very small number of breast cancers may arise from the muscle, fat, or connective tissues of the breast. Such cancers are known as sarcomas. The rare types of sarcoma that occasionally are diagnosed within the breast include:
- angiosarcoma (also known as hemangiosarcoma; a cancer that is composed of cavity-lining and fiber-producing cells), and
- cystosarcoma phylloides (a cancer that primarily affects middle-aged women who have histories of recurring fibroadenomas).
In addition, cancer can directly strike the lymphatic tissue within the breast, resulting in a primary lymphoma.