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What causes breast cancer?

No one knows for sure why some women get breast cancer while others do not. We do know, however, that certain factors can increase your risk of developing the disease. 

Risk factors that cannot be changed include:

  • Age—Your chances of getting breast cancer increase as you get older. Two out of three women with invasive cancer are diagnosed after age 55.
  • Gender—Breast cancer occurs nearly 100 times more often in women than in men. 
  • Family history and genetic factors—Having a close relative, such as a mother or sister, with breast cancer increase your risk. A family history of ovarian or prostate cancer is also a concern.
  • Genetic predisposition—Being a carrier for certain genes like BRCA1, BRCA2, and others increase your risk of developing the disease.
  • Race/ethnicity—White women develop breast cancer slightly more often than black women. However, black women tend to die more often of the disease. 
  • Personal factors—Starting a menstrual cycle before age 12 or going through menopause after age 55 increases risk.
  • Personal history—A previous history of breast cancer, benign breast disease or previous breast biopsy that showed tissue with atypical hyperplasia are risk factors. 
  • Radiation—Previous breast irradiation or therapeutic radiation to the chest increases risk. 

Lifestyle-related factors include:

  • Being overweight or obese—Excess weight can increase your risk of developing breast cancer, especially after menopause.
  • Hormone therapy—Using hormone replacement therapy after menopause can increase risk.
  • Taking birth control pills—Women using oral contraceptives have a slightly higher risk of breast cancer. This risk seems to decline once the pills are stopped.
  • Drinking alcohol—Excessive drinking can increase your risk of developing many cancers, including breast, throat, mouth, esophagus and liver. The American Cancer Society recommends that women have no more than one alcoholic drink a day.
  • Children—Women who have no children or who have their first child after age 30 have a slightly higher chance of developing breast cancer.

Anatomy of the breast

The breast is made up of fatty tissue, ducts, lobules, blood and lymph vessels.

  • Lobules—glands that make milk
  • Ducts—tubes that connect the lobules to the nipple
  • Fatty tissue—tissue that surrounds the lobules and ducts
  • Lymph vessels—vessels that carry lymph to nodes in the underarm, above the collarbone, and in the chest

The cells in the female breast have estrogen and progesterone hormone receptors and undergo many hormonally induced changes through their lifetime. Breast tissue primarily consists of glands during your reproductive years and swell with fluid on a cyclical basis. When you're pregnant, the lobules prepare to nourish your baby by producing milk. Hormone levels drop after menopause, which causes your breasts to lose their ability to produce milk. At this point, most of your glandular tissue will be replaced with less dense fatty tissue.

Are there different types of breast cancer?

There are different types of breast cancer that are classified by the tissue of origin and the degree of invasion of the surrounding tissue:

  • Ductal carcinoma in situ (DCIS)—the most common type of breast cancer, which begins in the lining of the ducts and does not spread outside the involved duct 
  • Lobular carcinoma in situ (LCIS)—which occurs in the lobules (milk-producing glands) and does not spread 
  • Invasive ductal carcinoma (IDC)—which starts in the milk ducts and then invades the surrounding tissue 

Breast cancers based on the degree of invasion of cancer in the surrounding tissue are:

  • Noninvasive (in situ) carcinoma, which does not extend beyond the involved duct or lobule
  • Invasive (infiltrating) carcinoma, which extends beyond its immediate surroundings into blood vessels, lymph channels or nerves in the breast tissue

Subtypes of invasive ductal carcinoma include:

  • Inflammatory breast cancer—A rare but aggressive form of breast cancer that starts in the breast and invades the skin and lymphatic system as it progresses. This type of cancer may cause inflammatory changes in the breast, mimicking 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 experiencing such breast changes should see a healthcare provider immediately.
  • Medullary carcinoma—This type of IDC is so-named because of its resemblance to the medulla brain tissue.
  • Tubular—A rare type of IDC that takes its name from its microscopic appearance.
  • Paget disease—A rare form of breast cancer that begins in the ducts but spreads to the skin of the nipple. More common in men than in women, it is often characterized by inflamed, red patches on the skin—usually an eczema-like rash appearing around the nipple.
  • Invasive lobular carcinoma—This is cancer that starts in the lobules and then invades the surrounding tissue, including the fatty tissue.
  • Mucinous (colloid) carcinoma—This very rare type of breast cancer produces mucous and has a good prognosis after treatment.
  • Triple negative breast cancer—A type of breast cancer wherein the cells are negative for estrogen receptor, progesterone receptor and HER2.
  • Male breast cancer—Breast cancer in men is rare, accounting for less than 1 percent of all breast cancer cases. Symptoms of male breast cancer include lumps, changes to the nipple or breast skin, or discharge of fluid from the nipple. The treatment of choice for male breast cancer is usually a mastectomy (surgery to remove the entire breast tissue). Other treatments include radiation, chemotherapy and/or hormone therapy.
  • Metastatic breast cancer—This is when breast cancer spreads from its site of origin to other organs of the body. The secondary tumor is the same as the primary tumor even though it is present in another organ. This may also be called "distant" disease. When breast cancer metastasizes or spreads outside the breast, cancer cells are often found in the lymph nodes under the arm. If cancer has reached these nodes, it may mean that cancer cells have spread to other parts of the body such as the liver, lungs and bones

What are the signs and symptoms of breast cancer?

Each individual may experience symptoms differently. Early breast cancer usually does not cause pain and may produce no symptoms. Some breast cancers never cause symptoms or other indications of a problem. As cancer grows, however, it can cause changes that women and men should watch for, such as:

  • A lump or thickening (a mass, swelling, skin irritation or distortion) in or near the breast or in the underarm area 
  • A change in the size or shape of the breast
  • A change in the color or feel of the skin of the breast, areola or nipple (dimpled, puckered, or scaly) 
  • Nipple discharge, erosion, inversion or tenderness 

If you notice any of these changes, you should consult your physician.

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