June 28th, 2012 by Hasham

Patient information: Risk factors for breast cancer

INTRODUCTION

About 210,000 women in the United States are diagnosed with breast cancer each year. However, not all women have the same risk of developing breast cancer during their lifetime. Studies have shown that certain factors, called risk factors, increase the likelihood that a woman will develop breast cancer. Many of these risk factors are not reversible, but some can be modified.

Not all factors increase a woman’s chance of developing breast cancer equally. Some factors (such as inheriting a breast cancer-related gene) increase a woman’s risk of breast cancer more than others (see ‘Strong risk factors’ below).

The presence of breast cancer risk factors does not mean that cancer is inevitable: many women with risk factors never develop breast cancer. Instead, risk factors help to identify women who may benefit most from screening or other preventive measures. Individual women should work with their clinicians to determine their own personal risk of breast cancer, based upon their own circumstances.

It is important to remember that breast cancer can also occur in women who have no identifiable risk factors. The average woman has about a 10 to 15 percent chance of developing breast cancer if she lives into her 90s. On the other hand, the risk of developing breast cancer in a woman with a strong family history of the disease who has inherited one of the genes that predispose her to breast cancer is over 50 percent. All women should discuss guidelines for breast cancer screening with their clinicians, even if they have a low risk for breast cancer based upon their risk factor profile.

This topic review discusses the individual factors that increase a woman’s risk of developing breast cancer and also reviews those factors that are thought to protect against the development of breast cancer.

STRONG RISK FACTORS

Unlike lung cancer, for which smoking is the biggest and most powerful risk factor, there is no single factor that is responsible for the majority of breast cancers in women. Nevertheless, there are three factors that strongly increase a woman’s risk of developing this disease: advancing age, family history of the disease, and a personal history of breast cancer.

Increasing age — The primary risk factor for breast cancer in most women is older age. Overall, 85 percent of cases occur in women 50 years of age and older, while only 5 percent of breast cancers develop in women younger than age 40. Most North American expert groups suggest that women over age 50 be screened for breast cancer every year. Breast cancer screening of women in their 40s and over the age of 70 is controversial.

Family history — Women who have a family history of breast or ovarian cancer are at a higher risk for breast cancer than those who lack such a history. Women who have an especially strong family history (eg, two or more first-degree relatives [a mother, daughter, or sister] with breast or ovarian cancer, particularly before menopause) have a greater than 50 percent chance of developing breast cancer. This represents an approximately five- to 10-fold increase in a woman’s baseline risk of developing breast cancer.

One of the main factors responsible for this elevated risk is an inherited genetic mutation in one of two genes, called BRCA1 and BRCA2. Genetic testing for the BRCA mutation is discussed in detail elsewhere.

Previous breast cancer — Women who have had cancer in one breast have an increased risk of developing cancer in the other breast. This is especially true if a woman has an inherited BRCA mutation. This fact underscores the need for close surveillance after treatment of a breast cancer, particularly in a woman who has inherited a BRCA mutation.

MODERATE RISK FACTORS

Five factors can modestly increase a woman’s risk of developing breast cancer (with the presence of each factor increasing the relative risk by 1.5- to 2-fold):

Density of the breasts on mammogram — Women whose mammograms show many dense areas of tissue have an increased risk of breast cancer compared to women whose mammograms reveal mainly fat tissue. A woman who is told that her mammogram has areas of increased density should ask her healthcare provider to explain what this means.

Biopsy abnormalities — Women who have had a prior breast biopsy that revealed a proliferative abnormality (excessive growth of the glandular breast tissue, also called hyperplasia) have an increased risk for breast cancer, particularly if the cells appear abnormal (atypical hyperplasia). Otherwise, benign breast conditions that are not proliferative (eg, fibrocystic change, or a noncomplex fibroadenoma) do not increase the risk of a woman developing breast cancer. Any woman who undergoes a biopsy of a breast abnormality needs to fully understand the results, particularly if they impact the frequency of breast cancer screening.

Exposure to radiation — Women who have undergone high-dose radiation therapy to the chest region, usually as part of cancer treatment, have an increased risk for breast cancer compared to women who have never had radiation therapy.

Breast Cancer Risk Factors

Every woman wants to know what she can do to lower her risk of breast cancer. Some of the factors associated with breast cancer — being a woman, your age, and your genetics, for example — can’t be changed. Other factors — maintaining a healthy weight, exercising, smoking cigarettes,  and eating nutritious food — can be changed by making choices. By choosing the healthiest lifestyle options possible, you can empower yourself and make sure your breast cancer risk is as low as possible.

The known risk factors for breast cancer are listed below. Click on each link to learn more about the risk factor and ways you can minimize it in your own life. If a factor can’t be changed (such as your genetics), you can learn about protective steps you can take that can help keep your risk as low as possible.

Reproductive history

Women in developed countries are at increased risk of breast cancer compared with women from less developed countries. A large part of this variation can be explained by the fact that women in developed countries have fewer children on average and a limited duration of breastfeeding.

Calculations based on breast cancer incidence rates during the 1990s suggest that the cumulative incidence of breast cancer in developed countries would be reduced by more than half, from 6.3 to 2.7 per 100, if woman had the average number of births(6.5 instead of 2.5 births) and lifetime duration of breastfeeding (breastfeed each child, on average, for 24 months instead of 8 months) typical in developing countries around that time

Risk factors

A risk factor is anything that makes it more likely you’ll get a particular disease. But having one or even several risk factors doesn’t necessarily mean you’ll develop cancer — many women who develop breast cancer have no known risk factors other than simply being women.

Being female. Women are much more likely than men are to develop breast cancer.
Increasing age. Your risk of breast cancer increases as you age. Women older than 55 have a greater risk than do younger women.
A personal history of breast cancer. If you’ve had breast cancer in one breast, you have an increased risk of developing cancer in the other breast.
A family history of breast cancer. If you have a mother, sister or daughter with breast cancer, you have a greater chance of being diagnosed with breast cancer. Still, the majority of people diagnosed with breast cancer have no family history of the disease.
Inherited genes that increase cancer risk. Certain gene mutations that increase the risk of breast cancer can be passed from parents to children. The most common gene mutations are referred to as BRCA1 and BRCA2. These genes can greatly increase your risk of breast cancer and other cancers, but they don’t make cancer inevitable.
Radiation exposure. If you received radiation treatments to your chest as a child or young adult, you’re more likely to develop breast cancer later in life.
Obesity. Being overweight or obese increases your risk of breast cancer because fat tissue produces estrogen that may help fuel certain cancers.
Beginning your period at a younger age. Beginning your period before age 12 increases your risk of breast cancer.
Beginning menopause at an older age. If you began menopause after age 55, you’re more likely to develop breast cancer.
Having your first child at an older age. Women who give birth to their first child after age 35 may have an increased risk of breast cancer.