What is Breast Cancer ?
Breast cancer is a malignant tumor that has developed from cells of the breast. The disease occurs mostly in women, but does occur rarely in men. The remainder of this document refers only to breast cancer in women.
Normal Breast Structure
The main components of the female breast are lobules (milk-producing glands), ducts (milk passages that connect the lobules and the nipple), and stroma (fatty tissue and ligaments surrounding the ducts and lobules, blood vessels, and lymphatic vessels).
Lymphatic vessels are similar to veins, except that they carry lymph instead of blood. Lymph is a clear fluid that contains tissue waste products and immune system cells. Cancer cells can enter lymph vessels. Most lymphatic vessels of the breast lead to axillary (underarm) lymph nodes.
Lymph nodes are small bean-shaped collections of immune system cells that are important in fighting infections. When breast cancer cells reach the axillary lymph nodes, they can continue to grow, often causing swelling of the lymph nodes in the underarm area. If breast cancer cells have grown in the axillary lymph nodes, they are more likely to have spread to other organs of the body as well. This is why finding out whether breast cancer has spread to axillary lymph nodes is important in selecting the best mode of treatment.
Benign Breast Lumps
Most breast lumps are benign, that is, not cancerous. Most lumps are caused by fibrocystic changes. Cysts are fluid-filled sacs, and fibrosis refers to connective tissue or scar tissue formation. Breast swelling and pain can be caused by fibrocystic changes. The breasts may feel nodular, or lumpy, and, sometimes, a clear or slightly cloudy nipple discharge is present. Benign breast tumors such as fibroadenomas or papillomas are abnormal growths, but they cannot spread outside of the breast to other organs.
Types of Breast Cancers
Understanding some of the key words used to describe different types of breast cancer is important because these types vary in their prognosis (the outlook for chances of survival) and their treatment options. An alphabetical list of terms, including the most common types of breast cancer, is given below:
Adenocarcinoma: This is a general type of cancer that starts in glandular tissues anywhere in the body. Nearly all breast cancers start in glandular tissue of the breast and, therefore, are adenocarcinomas. The two main types of breast adenocarcinomas are ductal carcinomas and lobular carcinomas.
Ductal carcinoma in situ (DCIS): Ductal carcinoma in situ (also known as intraductal carcinoma) is the most common type of noninvasive breast cancer. There are cancer cells inside the ducts but they have not spread through the walls of the ducts into the fatty tissue of the breast. Nearly 100% of women diagnosed at this early stage of breast cancer can be cured. The best way to find DCIS is with a mammogram. With more women getting mammograms each year, a diagnosis of DCIS is becoming more common. DCIS is sometimes subclassified based on its grade and type, in order to help predict the risk of cancer returning after treatment and to help select the most appropriate treatment. Grade refers to how aggressive cancer cells appear under a microscope. There are several types of DCIS, but the most important distinction among them is whether or not tumor cell necrosis (areas of dead or degenerating cancer cells) is present. The term comedocarcinoma is often used to describe a type of DCIS with necrosis.
Infiltrating (or invasive) ductal carcinoma (IDC): Starting in a milk passage, or duct, of the breast, this cancer has broken through the wall of the duct and invades the fatty tissue of the breast. At this point, it has the potential to metastasize, or spread, to other parts of the body through the lymphatic system and bloodstream. Infiltrating ductal carcinoma accounts for about 80% of invasive breast cancers.
Infiltrating (or invasive) lobular carcinoma (ILC): ILC starts in the milk-producing glands. Similar to IDC, this cancer has the potential to spread (metastasize) elsewhere in the body. About 10% to 15% of invasive breast cancers are invasive lobular carcinomas. ILC may be more difficult to detect by mammogram than IDC.
Inflammatory breast cancer: This rare type of invasive breast cancer accounts for about 1% of all breast cancers. Inflammatory breast cancer makes the skin of the breast look red and feel warm, as if it was infected and inflamed. The skin has a thick, pitted appearance that doctors often describe as resembling an orange peel. Sometimes the skin develops ridges and small bumps that look like hives. Doctors now know that these changes are not due to inflammation or infection, but the name given to this type of cancer long ago still persists. Cancer cells blocking lymph vessels or channels in the skin over the breast cause these symptoms.
In situ: This term is used for an early stage of cancer in which it is confined to the immediate area where it began. Specifically in breast cancer, in situ means that the cancer remains confined to ducts (ductal carcinoma in situ) or lobules (lobular carcinoma in situ). It has not invaded surrounding fatty tissues in the breast nor spread to other organs in the body.
Lobular carcinoma in situ (LCIS): While not a true cancer, LCIS (also called lobular neoplasia) is sometimes classified as a type of noninvasive breast cancer. It begins in the milk-producing glands, but does not penetrate through the wall of the lobules. Most breast cancer specialists think that LCIS, itself, does not become an invasive cancer, but women with this condition do have a higher risk of developing an invasive breast cancer in the same breast, or in the opposite breast. For this reason, it’s important for women with LCIS to have a physical exam two or three times a year, as well as an annual mammogram.
Medullary carcinoma: This special type of infiltrating breast cancer has a relatively well defined, distinct boundary between tumor tissue and normal tissue. It also has some other special features, including the large size of the cancer cells and the presence of immune system cells at the edges of the tumor. Medullary carcinoma accounts for about 5% of breast cancers. The outlook, or prognosis, for this kind of breast cancer is better than for other types of invasive breast cancer.
Mucinous carcinoma: This rare type of invasive breast cancer is formed by mucus-producing cancer cells. The prognosis for mucinous carcinoma is better than for the more common types of invasive breast cancer. Colloid carcinoma is another name for this type of breast cancer.
Paget’s disease of the nipple: This type of breast cancer starts in the breast ducts and spreads to the skin of the nipple and then to the areola, the dark circle around the nipple. It is a rare type of breast cancer, occurring in only 1% of all cases. The skin of the nipple and areola often appears crusted, scaly, and red, with areas of bleeding or oozing. The woman may notice burning or itching. Paget’s disease may be associated with in situ carcinoma, or with infiltrating breast carcinoma. If no lump can be felt in the breast tissue, and the biopsy shows DCIS but no invasive cancer, the prognosis is excellent.
Phyllodes tumor: This very rare type of breast tumor forms from the stroma (connective tissue) of the breast, in contrast to carcinomas which develop in the ducts or lobules. Phyllodes (also spelled phylloides) tumors are usually benign but on rare occasions may be malignant (having the potential to metastasize). Benign phyllodes tumors are successfully treated by removing the mass and a narrow margin of normal breast tissue. A malignant phyllodes tumor is treated by removing it along with a wider margin of normal tissue, or by mastectomy. These cancers do not respond to hormonal therapy and are not so likely to respond to chemotherapy or radiation therapy. In the past, both benign and malignant phyllodes tumors were referred to as cystosarcoma phyllodes.
Tubular carcinoma: Accounting for about 2% of all breast cancers, tubular carcinomas are a special type of infiltrating breast carcinoma. They have a better prognosis than usual infiltrating ductal or lobular carcinomas.
There is no certain way to prevent breast cancer. For now, the best plan for women at average breast cancer risk is to reduce risk factors whenever possible.
Breast cancer risk reduction with tamoxifen or raloxifene: Tamoxifen has been used for many years to reduce the risk of recurrence in localized breast cancer and as a treatment for advanced breast cancer. (See “How is Breast Cancer Treated?”) Results from the Breast Cancer Prevention Trial (BCPT) have shown that women at high risk for breast cancer are less likely to develop the disease if they take the antiestrogen drug, tamoxifen. After taking tamoxifen an average of 4 years, these women had 45% fewer breast cancers than women with the same risk factors who did not take tamoxifen.
Like tamoxifen, raloxifene also blocks the effect of estrogen on breast tissue. In a study to evaluate raloxifene as prevention for osteoporosis, the researchers also noticed that it also seemed to lower the risk of breast cancer. A study to compare the effectiveness of the two drugs, called the Study of Tamoxifen and Raloxifene or STAR trial, is currently underway. For now, raloxifene has not yet been approved for use in breast cancer risk reduction.
Prophylactic (preventive) mastectomy for women with very high breast cancer risk: Occasionally, a woman who is at very high risk for breast cancer will choose to have a prophylactic mastectomy. The purpose of the surgery is to reduce the risk by removing both breasts before breast cancer is diagnosed.
The reasons for considering this type of surgery may include one or more of the following risk factors:
Mutated BRCA genes found by genetic testing
Previous cancer in one breast, strong family history (breast cancer in several close relatives)
Biopsy specimens showing lobular carcinoma in situ (LCIS)
There is no way to know how this surgery would affect a particular woman. Some women with BRCA mutations will develop a fatal breast cancer early in life, and a prophylactic mastectomy before cancer occurred might have added many years to their life expectancy. Some women with BRCA mutations never develop breast cancer, and these women would not benefit from the surgery. Still other women might develop breast cancer that can be found by mammography or breast examination, and be successfully treated; these women’s life expectancies would also not be affected by the operation. It is important to realize that while this operation removes nearly all of the breast tissue, a small amount remains. So, while, this operation markedly reduces the risk of breast cancer, it does not guarantee that a cancer will not develop in the small amount of breast tissue remaining after surgery.
Second opinions are strongly recommended before any woman makes the decision to have this surgery. The American Cancer Society Board of Directors has stated that “only very strong clinical and/or pathologic indications warrant doing this type of “preventive operation.” Nonetheless, after careful consideration, this might be the right choice for some women.