Many factors can influence a woman's risk of getting breast cancer, but having one or more risk factors does not necessarily mean that a woman What Are the Risk Factors for Breast Cancer? | Breast Cancer Prevention | Imaginis - The Women's Health & Wellness Resource Network

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What Are the Risk Factors for Breast Cancer?

Many factors can influence a woman's risk of getting breast cancer, but having one or more risk factors does not necessarily mean that a woman will get breast cancer. Some women with one or more breast cancer risk factors never develop the disease, while the majority of women with breast cancer have no apparent risk factors. Even when a woman has a risk factor, there is no way to prove that it was the actual cause of breast cancer.

Risk Factors for Breast Cancer

Risk Factors for Breast Cancer Include Both Those That Can Not be Changed Such As Genetics and Age, and Those That Can Be Changed Such As Lifestyle:

Age: As a woman ages, her risk of breast cancer also increases. About 77% of women with breast cancer are over age 50 at the time of diagnosis. Three quarters of women with breast cancer are over age 50 at the time of diagnosis. Women between the ages of 20 and 29 account for only 0.3% of breast cancer cases.

 A Woman's Chances of Breast Cancer Increases With Age 
From age 30 to age 39 0.44% (1 in 227)
From age 40 to age 49 1.49% (1 in 67)
From age 50 to age 59 2.79% (1 in 36)
From age 60 to age 70 3.38% (1 in 26)

Source: National Cancer Institute,, 2004.

This risk model is based on population averages. Each woman's breast cancer risk may be higher or lower, depending upon a several factors, including family history, genetics, age of menstruation, and other factors that have not yet been identified. See the "Understanding the One-in-Seven Statistic" section below for more information.

Genetics: Changes (or mutations) of certain genes may cause some cells to become cancerous. Recent studies have shown that up to 10% of breast cancer cases are hereditary. In 1994, researchers discovered that women who carry mutations of BRCA1 (breast cancer gene 1) or BRCA2 (breast cancer gene 2) are at higher risk of developing both breast and ovarian cancer than women who do not have these genetic mutations. Currently, women with BRCA1 mutations account for 5% of all breast cancer cases. Jewish women of Northeastern European decent (Ashkenazie women) have a higher prevalence of BRCA1.

HER2 (human epidermal growth factor receptor 2) is another gene found on the surface of cells that plays a key role in regulating cell growth. When the HER2 gene is altered, extra HER2 receptors may be produced. This over-expression of HER2 causes increased cell growth and reproduction, often resulting in more aggressive tumor cells. HER2 protein over-expression affects 25% to 30% of breast cancer patients. The U.S. Food and Drug Administration (FDA) has recently approved the drug, Herceptin, to use in some breast cancer patients with HER2 abnormalities.

Mutations of the p53 gene may also increase a woman’s risk of breast cancer. Recent studies have revealed that that women with early-stage breast cancer who test positive for the mutated p53 tumor suppressor tend to have a poorer breast cancer prognosis (outcome) than women who do not carry the mutated p53.

Click here to learn more about genetic risk factors for breast cancer.

Personal history: Women who have had breast cancer in one breast are three to four times as likely to develop breast cancer in the opposite breast than women who have never had breast cancer.

Family history: If a woman’s blood-related relatives on either her mother or father’s side of the family have had breast cancer, then she is at increased risk for the disease. Having a first-degree relative (mother, sister, daughter) with breast cancer can double a woman’s risk.

The following conditions increase breast cancer risk:

  • Two or more relatives with breast or ovarian cancer.
  • Breast cancer occurs before age 50 in a relative (mother, sister, grandmother or aunt) on either side of the family. The risk is higher if the mother or sister has a history of breast cancer.
  • Relatives with both breast and ovarian cancer
  • One 1 or more relatives with two cancers (breast and ovarian, or two different breast cancers)
  • A male relative (or relatives) with breast cancer
  • A family history of breast or ovarian cancer and Ashkenazi Jewish heritage.
  • A family history includes a history of diseases associated with hereditary breast cancer such as Li-Fraumeni or Cowdens Syndromes

Source: American Cancer Society,, 2004.

Previous breast biopsy showing benign conditions: Women who have previously had breast biopsies showing benign (non-cancerous) conditions such as lobular carcinoma in situ (LCIS) or atypical hyperplasia (AH) may have a slightly higher risk of developing breast cancer. These conditions are characterized by a sharp increase in the number of breast cells. Women with fibrocystic change are not at increased risk for breast cancer (symptoms of fibrocystic breasts include lumpiness, tenderness, areas of thickening, cysts, or breast pain).

Menstrual periods: Women who begin menstruating at an early age (before age 12) and those who reach menopause after age 55 have an increased risk of breast cancer.

Delayed childbirth: Women who have their first child after age 30 or who never have a child are at a slightly higher risk for developing breast cancer.

Alcohol: Most healthcare provides agree that alcohol consumption can increase the risk of breast cancer. In a 2002 study, researchers analyzed dietary and beverage habits of over 60,000 women and found that those who consumed alcohol had a 30% higher risk of developing breast cancer, compared to women who did not drink.

Smoking: Smoking increases a woman’s chance of developing several types of cancer, including breast cancer.

Diet: There is a much higher incidence of breast cancer in areas with high fat diets (such as the United States) than areas with low-fat diets (such as Japan). However, the link between diet and breast cancer risk is complicated and is affected by the type of fat in a woman’s diet. Monounsaturated fats, such as canola oil or olive oil have been linked to lower breast cancer risk while a diet high in polyunsaturated fats such as corn oils, tub margarine, and saturated fats in meats are associated with a higher risk of breast cancer.

In February 2006, results of a large U.S. federally-funded study found that a low-fat diet does not appear to significantly lower the risk of breast cancer or other diseases. Despite the widely publicized and seemingly disappointing results, the study did find a 9% reduction in breast cancer risk among the post-menopausal women who followed a low-fat diet-a promising finding but one too small to be considered statistically significant. The study also showed that a low-fat diet was associated with a statistically significant 15% reduction in estradiol, a form of blood estrogen that increases the risk of breast cancer. The researchers concluded that while switching to a low-fat diet may reduce breast cancer risk for some women, they do not have enough data to make a broad recommendation concerning diet at this time.

Weight: The link between weight and breast cancer risk is controversial. Some studies suggest that overweight (obese) women who gained weight as adults are at an increased risk of developing breast cancer, but women who have been overweight since childhood are not at any significantly higher risk. Also, overweight women who take hormone replacement therapy maybe at greater risk of developing breast cancer.

Previous radiation therapy: Women whose breast/chest area have been exposed to radiation therapy during childhood are at higher risk of developing breast cancer, especially if radiation was used to treat Hodgkin’s disease. In general, the younger the woman was exposed to radiation, the greater the risk that she will develop breast cancer.

Hormone replacement therapy (HRT): Although studies have been inconsistent, there appears to be an emerging consensus that the use of hormone replacement therapy (HRT) increases the risk of breast cancer. In July 2002, the National Institutes of Health halted a large study on HRT, called the Women's Health Initiative, because the combined estrogen/progestin regimen of the therapy was found to cause 8 cases of invasive breast cancer for every 10,000 women on HRT (a 26 percent increase in breast cancer risk compared to women who do not take HRT). Further, in December 2006, researchers studying the incidence of breast cancer in the United States found a sharp decrease in the number of cases between 2002 and 2003-the time period when the results of the Women's Health Initiative were announced. The researchers did not study the causes associated with the decline in breast cancer cases and therefore cannot say whether the decrease was linked to the reduction in HRT use. Though these results can be alarming, some experts believe that limited, short-term use of HRT can be safe among some women with severe menopausal symptoms who are not at high risk of breast cancer or other diseases. Women considering HRT should discuss the benefits and risks with a physician.

Click here to learn more about HRT.