Understanding Breast Cancer -- the Basics

What Is Breast Cancer?

Before discussing breast cancer, it's important to be familiar with the anatomy of the breast. The normal breast consists of milk-producing glands that are connected to the surface of the skin at the nipple by narrow ducts. The glands and ducts are supported by connective tissue made up of fat and fibrous material. Blood vessels, nerves, and lymphatic channels to the lymph nodes make up most of the rest of the breast tissue. This breast anatomy sits under the skin and on top of the chest muscles.

As in all forms of cancer, the abnormal tissue that makes up breast cancer is the patient's own cells that have multiplied uncontrollably. Those cells may also travel to locations in the body where they are not normally found. When that happens, the cancer is called metastatic.

Breast cancer develops in the breast tissue, primarily in the milk ducts (ductal carcinoma) or glands (lobular carcinoma). The cancer is still called and treated as breast cancer even if it is first discovered after the cells have travelled to other areas of the body. In those cases, the cancer is referred to as metastatic or advanced breast cancer.

Breast cancer usually begins with the formation of a small, confined tumor (lump), or as calcium deposits (microcalcifications) and then spreads through channels within the breast to the lymph nodes or through the blood stream to other organs. The tumor may grow and invade tissue around the breast, such as the skin or chest wall. Different types of breast cancer grow and spread at different rates -- some take years to spread beyond the breast while others grow and spread quickly.

Some lumps are benign (not cancerous), however some of these can be premalignant. The only safe way to distinguish between a benign lump and cancer is to have the tissue examined by a doctor through a biopsy.

Breast Cancer

Men can get breast cancer, too, but they account for just one percent of all breast cancer cases. Among women, breast cancer is the most common cancer and the second leading cause of cancer deaths after lung cancer.

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If eight women were to live to be at least 85, one of them would be expected to develop the disease at some point during her life. Two-thirds of women with breast cancer are over 50, and most of the rest are between 39 and 49.

Fortunately, breast cancer is very treatable if detected early. Localized tumors can usually be treated successfully before the cancer spreads; and in nine out of 10 cases, the woman will live at least another five years. However, late recurrences of breast cancer are common.

Once the cancer begins to spread, treatment becomes difficult, although treatment can often control the disease for years. Improved screening procedures and treatment options mean about 8 out of 10 women with breast cancer will survive at least 10 years after initial diagnosis.

 

What Causes Breast Cancer?

Although the precise causes of breast cancer are unclear, we know what the main risk factors are. Still, most women considered at high risk for breast cancer do not get it. On the other hand, 75% of women who develop breast cancer have no known risk factors. Among the most significant factors are advancing age and family history. Risk increases slightly for a woman who has certain benign breast lumps and increases significantly for a woman who has previously had breast cancer or endometrial, ovarian, or colon cancer.

A woman whose mother, sister, or daughter has had breast cancer is two to three times more likely to develop the disease, particularly if more than one first-degree relative has been affected. This is especially true if the cancer developed in the woman while she was premenopausal, or if the cancer developed in both breasts. Researchers have now identified two genes responsible for some instances of familial breast cancer -- BRCA1 and BRCA2. About one woman in 200 carries one of these genes. Having a BRCA1 or BRCA2 gene predisposes a woman to breast cancer, and while it does not ensure that she will get breast cancer, her lifetime risk is 45% – 80%. These genes also predispose to ovarian cancer and are associated with pancreas cancer, melanoma, and male breast cancer (BRCA2).

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Because of these risks, prevention strategies and screening guidelines for those with the BRCA genes are more aggressive. There are other genes that have been identified as increasing the risk of breast cancer, including the PTEN gene, the ATM gene, the TP53 gene, and the CHEK2 gene. However, these genes carry a lower risk for breast cancer development than the BRCA genes.

Generally, women over 50 are more likely to get breast cancer than younger women, and African-American women are more likely than Caucasians to get breast cancer before menopause.

A link between breast cancer and hormones is clear. Researchers think that the greater a woman's exposure to the hormone estrogen, the more susceptible she is to breast cancer. Estrogen tells cells to divide; the more the cells divide, the more likely they are to be abnormal in some way, potentially becoming cancerous.

A woman's exposure to estrogen and progesterone rises and falls during her lifetime. This is influenced by the age she starts menstruating (menarche) and stops menstruating (menopause), the average length of her menstrual cycle, and her age at first childbirth. A woman's risk for breast cancer is increased if she starts menstruating before age 12 (less than 2 times the risk), has her first child after 30, stops menstruating after 55, or does not breast feed. Current information about the effect of birth control pills and breast cancer risk is mixed. Some studies have found that the hormones in birth control pills probably do not increase breast cancer risk or protect against breast cancer. However other studies suggest that the risk of breast cancer is increased in women who have taken birth control pills recently, regardless of how long she has taken them.

Some studies suggest that the use of hormone replacement therapy with combined estrogen and progesterone containing compounds increases the risk of developing breast cancers. They also show, after a 7 year follow up, that the use of estrogens alone does not increase or decrease the risk of breast cancer development. Their use may, though, increase the risk of clotting.

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High doses of radiation, such as with nuclear exposure, or therapeutic radiation, such as used for Hodgkin lymphoma, are a factor for breast cancer development after15-20 years. Mammography poses almost no risk of breast cancer development.

The link between diet and breast cancer has been debated. Obesity is a noteworthy risk factor, predominately in postmenopausal women, because obesity alters a woman's estrogen metabolism. Drinking alcohol regularly -- particularly more than one drink a day -- also increases the risk of breast cancer. Many studies have shown that women whose diets are high in fat, either from red meat or high-fat dairy products, are more likely to get the disease. Researchers suspect that if a woman lowers her daily calories from fat -- to less than 20-30 percent -- her diet may help protect her from developing breast cancer.

 

WebMD Medical Reference Reviewed by Laura J. Martin, MD on July 18, 2017

Sources

SOURCES:

American Cancer Society: "Learn about Cancer: Breast Cancer."

National Cancer Institute: "Breast Cancer."

CDC: "Breast Cancer."

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