Breast cancer is the most common cancer in women, other than skin cancer, and the second deadliest cancer in U.S. women; lung cancer is the deadliest. Approximately 207,090 cases of invasive breast cancer will be diagnosed in 2010, according to the American Cancer Society (ACS). Though an estimated 39,840 women will die from breast cancer, there are more than 2.5 million breast cancer survivors in the United States, according to the ACS.
Fortunately, the number of deaths caused by breast cancer has declined significantly in recent years, with the largest decreases in younger women—both Caucasian and African American. These decreases are probably the result of earlier detection and improved treatment.
In 2003, The National Cancer Institute found a significant drop in the rate of hormone-dependent breast cancers among women, the most common breast cancer. In a study published in late 2006, researchers speculated that the drop was directly related to the fact that millions of women stopped taking hormone replacement therapy (HRT) in 2002 after a major government study found the treatment slightly increased a woman's risk for breast cancer, heart disease and stroke. The researchers suggested that stopping the treatment slowed the growth of very tiny cancers into larger tumors that could be detected because they didn't have the additional estrogen required to fuel their growth.
Breast cancer is a disease in which malignant (cancerous) cells are found in breast tissues. Each breast has 15 to 20 sections called lobes, which have many smaller sections called lobules. The lobes and lobules are connected by thin tubes called ducts.
One of the most important factors when it comes to breast cancer is whether the cancer is invasive or noninvasive. Noninvasive (in situ) cancers are confined to the ducts or lobules and have not spread to surrounding tissues or other parts of the body. Noninvasive cancers can develop into more serious invasive tumors. Invasive breast cancer has spread outside the milk duct and into the normal tissue inside the breast. Whether a breast cancer is invasive or noninvasive determines treatment and prognosis.
The different kinds of breast cancer that involve the lobes, lobules and/or ducts are:
Ductal carcinoma in situ (DCIS). Also known as intraductal carcinoma or noninvasive breast cancer, DCIS is confined to the ducts and has not invaded surrounding tissue. As the use of screening mammography has increased in the United States, the frequency of DCIS diagnosis has increased significantly. It is the most common subgroup of noninvasive breast cancer; one out of five cases of breast cancer is DCIS.
Invasive ductal cancer. Also called infiltrating ductal carcinoma, this type of breast cancer is the most common of all breast cancers. It makes up about 80 percent of all newly diagnosed cases of invasive breast cancer. It is found in the cells of the ducts and is usually a hard lump.
Invasive lobular carcinoma. This form of breast cancer occurs at the ends of the ducts or in the lobules and accounts for 10 percent of invasive breast cancers.
Less common types of breast cancer:
Mucinous carcinoma (colloid carcinoma). A rare type of invasive breast cancer, mucinous carcinoma is formed by mucin-producing cancer cells. Prognosis for this type of invasive breast cancer is generally better than for other more common types.
Medullary carcinoma. This type of breast cancer accounts for 3 to 5 percent of all breast cancers and involves a distinct boundary between tumor tissue and normal tissue. It also differs from other forms of invasive ductal cancers in that it contains large cancer cells and immune system cells throughout the tumor. The prognosis for this type of cancer is generally better than for other invasive forms.
Tubular carcinoma. Tubular carcinoma is characterized by tubular structures ringed with a single layer of cells. Only 2 percent of all breast cancers fall into this category. The prognosis is usually good.
Paget's disease. A rare breast cancer in the ducts beneath the nipple accounting for only 1 percent of cases, invasive Paget's disease starts with an itchy, eczema-like rash around the nipple. Paget's disease can be associated with a noninvasive or invasive underlying mass. For noninvasive cases, it is believed that the cells have migrated from the ducts of the nipple to the nipple's epidermis, though this is still under study.
Inflammatory carcinoma. This aggressive type of breast cancer accounts for 1 to 3 percent of all cases. Skin over the breast appears acutely inflamed and swollen because skin lymph vessels are blocked by cancer.
Triple-negative breast cancer. This type of breast cancer, usually invasive ductal carcinoma, has cells that lack receptors for the hormones estrogen and progesterone, and it does not express a specific protein called HER2, which makes tumors grow quickly. Triple-negative breast cancers tend to occur in younger women and Africa-American women and spread more quickly than most other breast cancer types.
Metaplastic carcinoma. Also called carcinoma with metaplasia, this is a very rare type of invasive ductal breast cancer. These tumor cells make tissue not normally found in the breast such as bone and even cartilage and are treated like invasive ductal cancer.
Papillary carcinoma. This type of breast cancer, which can be separated into noninvasive and invasive types, includes cells arranged in small, fingerlike projections. These cancers are more common in older women and make up no more than 1 to 2 percent of all breast cancers.
Mixed tumors. Mixed breast tumors contain a variety of cell types, such as invasive lobular breast cancer combined with invasive ductal cancer.
Adenoid cystic carcinoma (adenocystic carcinoma). These breast cancers have both cylinder-like (cystic) and glandular (adenoid) features and make up less than 1 percent of breast cancers. Because they rarely spread to the lymph nodes and distant areas, these tumors usually have a very good prognosis.
Phyllodes tumor. A very rare form of breast cancer, phyllodes tumor forms in the connective tissue of the breast, called the stroma. Phyllodes tumors are usually benign but may be malignant in rare cases.
Angiosarcoma. This form of breast cancer begins in cells that line blood vessels or lymph vessels. It rarely forms in the breast, but when it does, it usually forms as a result of previous radiation treatment five to 10 years later