What causes Breast Cancer?

Breast cancer affects one in eight women during their lives. It kills more women in the United States than any cancer except lung cancer. (Source: NIH: National Cancer Institute)

The reasons why some women get breast cancer while others do not remain unclear. However, there are certain factors that can increase your risk of developing the disease. 

Factors that cannot be changed include:
  • Age - the chance of getting breast cancer increases 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 increases your risk. This includes changes in certain genes such as BRCA1, BRCA2, and others. A family history of ovarian or prostate cancer is also a concern.
  • Race/ethnicity - White women develop breast cancer slightly more often than black women. However, black women tend to die of breast cancer more often. 
  • Personal factors - starting a menstrual cycle before age 12 or going through menopause after age 55.
  • A personal history of breast cancer, benign breast disease or previous breast biopsy that showed tissue with atypical hyperplasia. 
  • Previous breast irradiation or therapeutic radiation to the chest. 

Lifestyle-related factors include:
  • Being overweight or obese - This can increase your risk for developing breast cancer, especially after menopause.
  • Using hormone replacement therapy after menopause.
  • 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 also increase your risk of developing cancers of the mouth, throat, esophagus and liver. The American Cancer Society recommends that women have no more than one alcoholic drink a day.
  • Having children - Women who have no children or who have their first child after age 30 have a slightly higher chance of developing breast cancer.

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: surrounds the lobules and ducts.

Lymph vessels: carry lymph to lymph 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 the lifetime. Breast tissues primarily consist 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. The hormone levels drop after menopause, which cause 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.

What are the different types of breast cancer?

There are different types of breast cancer depending on the tissue of origin and the degree of invasion of the surrounding tissue:

  1. Breast Cancers based on the tissue of origin: 
    1. Ductal Carcinoma originates in the ducts 
    2. Lobular Carcinoma begins in the milk producing lobules
  2. Breast Cancers based on the degree of invasion of cancer in the surrounding tissue:
    1. Noninvasive (in-situ) carcinoma: Cancer that does not extend beyond the involved duct or the lobule is called in-situ carcinoma.
    2. Invasive or Infiltrating Carcinoma: Occasionally the cancer extends beyond its immediate surroundings and is called invasive or infiltrating cancer. Sometimes breast cancer can invade the blood vessels, lymph channels (lymphovascular invasion) or nerves (perineural invasion) in the breast tissue.
  • Ductal Carcinoma in Situ (DCIS): This is 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) : This is another common type that occurs in the lobules (milk-producing glands). 
  • Invasive Ductal Carcinoma (IDC) : Cancer that starts in the milk ducts and then invades the surrounding tissue. Subtypes include:
    • Inflammatory Breast Cancer: This is 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 cancers may present with 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: Type of IDC that is so-named because of its resemblance to the brain tissue (medulla).
    • Tubular: It is a rare type of IDC that takes its name from its microscopic appearance.
    • Paget's disease: A rare form of breast cancer that begins in the ducts, but spreads to the nipple of the skin. 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 (ILC) : Cancer that starts in the lobules and then invades the surrounding tissue including the fatty tissue.
  • Mucinous (colloid) carcinoma :  This is a very rare type of breast cancer that produces mucous and has a good prognosis after treatment.
  • Triple Negative Breast Cancer : A type of breast cancer is a type of breast cancer where 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% of all breast cancer cases (Source: Cancer.Net). 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 : When breast cancer spreads from its site of origin (Primary Cancer) to other organs of the body, it is called metastatic breast cancer. This 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 the 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?

The following are the most common symptoms of breast cancer. However, each individual may experience symptoms differently. Early breast cancer usually does not cause pain and may produce no symptoms. And, some breast cancers never cause symptoms or other indications of a problem. As the 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. 
  • A woman (or man) should consult a physician when any of these changes are noticed.