What Causes Breast Cancer
Breast cancer is caused when the DNA in breast cells mutate or change, disabling specific functions that control cell growth and division. In many cases, these mutated cells die or are attacked by the immune system. But some cells escape the immune system and grow unchecked, forming a tumor in the breast.
The key to lowering your risk for breast cancer is to focus most of your prevention efforts on those modifiable risk factors, and to be proactive in various ways to monitor the ones you cant change.
Being Overweight Or Obese
Women who are overweight after their menopause have a higher risk of breast cancer than women who are not overweight. Men also have an increased risk of breast cancer if they are overweight or obese. For both men and women, the risk increases as more weight is gained.
Body mass index is a measure that uses your height and weight to work out whether you are a healthy weight. For most adults, an ideal is between 18.5 to 24.9. Being overweight means having a BMI of between 25 and 30. Obesity means being very overweight with a BMI of 30 or higher.
Try to keep a healthy weight by being physically active and eating a healthy, balanced diet.
Drinking alcohol increases the risk of breast cancer in women. The risk increases with each extra unit of alcohol per day. The number of units in a drink depends on the size of the drink, and the volume of alcohol.
The latest UK government guidelines advise drinking no more than 14 units of alcohol a week.
How Has The Risk Of Being Diagnosed With Breast Cancer Changed In Recent Years
For a woman born in the 1970s in the United States, the lifetime risk of being diagnosed with breast cancer, based on breast cancer statistics from that time, was just under 10% .
The last five annual SEER Cancer Statistics Review reports show the following estimates of lifetime risk of breast cancer, all very close to a lifetime risk of 1 in 8:
- 12.83%, based on statistics for 2014 through 2016
- 12.44%, based on statistics for 2013 through 2015
- 12.41%, based on statistics for 2012 through 2014
- 12.43%, based on statistics for 2011 through 2013
- 12.32%, based on statistics for 2010 through 2012
SEER statisticians expect some variability from year to year. Slight changes may be explained by a variety of factors, including minor changes in risk factor levels in the population, slight changes in breast cancer screening rates, or just random variability inherent in the data.
Howlader N, Noone AM, Krapcho M, et al. . SEER Cancer Statistics Review, 19752017, National Cancer Institute. Bethesda, MD, , based on November 2019 SEER data submission, posted to the SEER web site, April 2020.
- Reviewed:December 16, 2020
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Being Female And Getting Older
Unfortunately, being a woman and getting older are the highest risk factors for developing breast cancer. 99% of all breast cancer cases occur in women, and around 75% of all breast cancer cases occur in women over 50 years. As a woman ages, its more likely that abnormal changes might occur in her breasts. Men can get breast cancer too, but their risk is much lower and they account for only 1% of all cases.
Differences By Race And Ethnicity
Some variations in breast cancer can be seen between racial and ethnic groups. For example,
- The median age of diagnosis is slightly younger for Black women compared to white women 63 years old).
- Black women have the highest death rate from breast cancer. This is thought to be partially because about 1 in 5 Black women with breast cancer have triple-negative breast cancer – more than any other racial/ethnic group.
- Black women have a higher chance of developing breast cancer before the age of 40 than white women.
- At every age, Black women are more likely to die from breast cancer than any other race or ethnic group.
- White and Asian/Pacific Islander women are more likely to be diagnosed with localized breast cancer than Black, Hispanic, and American Indian/Alaska Native women.
- Asian/Pacific Islanders have the lowest death rate from breast cancer.
- American Indian/Alaska Natives have the lowest rates of developing breast cancer.
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Hereditary Breast And Ovarian Cancer
About 5% to 10% of breast and 10% to 15% of ovarian cancers are hereditary. Hereditary cancer means cancer runs in your family, and could be caused by a change in certain genes that you inherited from your mother or father.
Genes act as instructions and contain information to build and maintain cells in the body. Humans inherit one set of genes from their mother and one set of genes from their father.
Genes are made up of DNA. DNA tells the body what traits will be passed on from parents to children, such as blood type, hair color, eye color, and risks of getting certain diseases.
Risk According To Breast Cancer Risk Factor Profile
The risk associated with postmenopausal hormone use was assessed in a number of specific subgroups in the pooled analysis. Risk did not appear to vary according to reproductive history, alcohol intake, smoking history, or family history of breast cancer.
However, the RRs associated with 5 or more years of postmenopausal hormone use were highest among the leanest women this interaction has been consistently observed. Risk of unopposed estrogen therapy is also more clearly observed to increase with duration of use among women with bilateral oophorectomy than those without, again consistent with precise statistical control for underlying risk of breast cancer, as age at menopause is more accurately assessed in women undergoing bilateral oophorectomy than in those who have hysterectomy without oophorectomy. This consistent finding that risk of unopposed estrogen is attenuated among overweight and obese women may account for the apparent lower risk of breast cancer among women in the WHI trial of unopposed estrogen, given the overweight and obese population included in the trial.
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Why Is Screening So Important
While some tumors in the breast are aggressive and grow quickly, most grow slowly. In some cases a tumor may have been growing for as long as 10 years before it creates a lump large enough to feel. That means that even if you know whats normal for your breasts and notice when something changes, you may not feel anything until the cancers been growing for a while.
Screening tests can find breast cancer early, when the chances of survival are highest. They can find breast cancer in a person who doesnt have any early signs or symptoms. For people at a higher risk, more frequent screening can mean that if they do develop cancer, they can find it and treat it sooner.
Breast And Ovarian Cancer And Family Health History
If you are a woman with a family health history of breast cancer or ovarian cancer, you may be more likely to get these cancers yourself. Collecting your family health history of breast, ovarian, and other cancers and sharing this information with your doctor can help you find out if youre at higher risk. If you have had breast, ovarian, or other cancers, make sure that your family members know about your diagnosis.
Your doctor might consider your family health history in deciding when you should start mammography screening for breast cancer. If you are a woman with a parent, sibling, or child with breast cancer, you are at higher risk for breast cancer. Based on current recommendations, you should consider talking to your doctor about starting mammography screening in your 40s. In some cases, your doctor might recommend that you have genetic counseling, and a genetic counselor might recommend genetic testing based on your family health history. Breast, ovarian, and other cancers are sometimes caused by inherited mutations in BRCA1, BRCA2, and other genes. The genetic counselor can help determine which genetic mutations you should be tested for, based on your personal and family health history of cancer, ancestry, and other factors.
When collecting your family health history:
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Absolute Risk And Relative Risk
Understanding the terms absolute risk and relative risk can help people better understand their own breast cancer risk.
Absolute risk refers to a persons risk of developing a disease, such as breast cancer, over a defined period of time. For example, the National Cancer Institute is referring to absolute risk when it reports that the average U.S. woman has a 12.9% risk of developing breast cancer in her lifetime.
Relative risk compares risk in two different groups of people. Relative risk also shows how someones behavior can change their risk compared with their absolute risk.
For example, a 2017 study found that women who started smoking before age 17 had a 24% higher risk of developing breast cancer. This 24% increase in risk is relative risk. It doesnt mean that women who start smoking before age 17 have a 24% risk of developing breast cancer in their lifetime. It means the risk is 24% higher than the average risk of 12.9%.
To figure out the increase in absolute risk, we have to do some math: 24% of 12.9% is 3% . So a woman who starts smoking before age 17 has a 3% increase in absolute risk, which means her lifetime risk of developing breast cancer is 15.9% .
Relative risk can be confusing because many people focus on the increase in risk and assume its an increase in absolute risk.
An increase of 24% sounds alarming. But its important to remember that this increase is relative to the average risk of developing breast cancer.
Breast cancer risk can also decrease.
Risk Of Breast Cancer In Different Countries
The above information and statistics are based on American women. However, the risk of breast cancer is not the same around the world.
In Canada, based on the Canadian Cancer Society 2010 data, the lifetime risk of breast cancer is around 1 in 9 or 11%. Furthermore, 1 in 30 will die from breast cancer.
For women in the UK, the risk of breast cancer diagnosis in a lifetime, according to statistics from Cancer Research UK in 2012, is also 1 in 8.
According to the Australian government data for 2017, a womans risk of breast cancer by the time they are 85, is 1 in 14.
Because the incidence of breast cancer is lower in Asia compared to Western countries, the lifetime risk is currently lower too. For women of Malaysia, the risk of breast cancer is 1 in 28. For Chinese women, it is 1 in 16 and for Indian women, it is a 1 in 17 risk.
These figures are, however, a little old based on statistics from 2003 to 2005. Indeed, incidence rates of breast cancer in parts of Asia have been rapidly rising, so expect the lifetime risk to be higher too.
Interestingly, when a woman from a country with a low risk moves to a higher risk country her lifetime risk of breast cancer changes to that of the country she has moved to.
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Family History And Inherited Genes
Some people have a higher risk of developing breast cancer than the general population because other members of their family have had particular cancers. This is called a family history of cancer.
Having a mother, sister or daughter diagnosed with breast cancer increases the risk of breast cancer. This risk is higher when more close relatives have breast cancer, or if a relative developed breast cancer under the age of 50. But most women who have a close relative with breast cancer will never develop it.
Some people have an increased risk of breast cancer because they have an inherited gene fault. We know about several gene faults that can increase breast cancer risk and there are tests for some of them. Having one of these faulty genes means that you are more likely to get breast cancer than someone who doesnt. But it is not a certainty.
Two of these faulty genes are known as BRCA1 and BRCA2. These are not common. Only about 2 out of every hundred of breast cancers are related to a change in the BRCA1 or BRCA2 genes.
Ionising radiation includes tests such as x-rays and CT scans and treatment such as radiotherapy.
A Healthy Lifestyle Can Reduce Breast Cancer Risk For All Women
Healthy behaviors also play a big role in breast cancer cases.
“Hispanic and Asian womens risk changes when they come from their native country to the United States and are exposed to this country’s sedentary lifestyle and fattening diet, says Bevers.
For example, breast cancer risk is not very high in Asian women. If they come to the United States and adopt the lifestyle, their breast cancer risk increases. The same is true of Hispanic women who move from their native countries and adopt an American lifestyle.
Race is only one factor that affects your breast cancer risk. Lifestyle choices also play a role. There are steps women of all races can take to reduce their breast cancer risk.
Maintain a healthy weight, especially after menopause. Being overweight or obese raises your risk for a number of cancers, including breast cancer.
Avoid alcohol. If you choose to drink, limit yourself to one drink per day. Alcohol raises risk for several types of cancers, so men should limit themselves to two drinks per day.
Exercise. Women who are physically active have a lower-than-average risk of breast cancer. Women who are not active have a higher-than-average risk. Aim for 150 minutes of moderate activity or 75 minutes of vigorous activity a week.
Manage hormones naturally. Using hormone therapy during menopause increases your risk of breast cancer and possibly ovarian cancer.
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Trends In Incidence And Mortality Around The World
Since the 1950s, breast cancer incidence has been increasing in many of the lower-risk countries, as well as in high-risk Western countries. Some of the recent increases in incidence in high-risk populations may be due in part to greater use of mammography, as in the United States. This appears to be the case in Sweden and in England and Wales. However, in Norway, a substantial increase in breast cancer incidence occurred between 1983 and 1993 despite low use of mammographic screening.
Breast cancer incidence rates have nearly doubled in recent decades in traditionally low-risk countries such as Japan and Singapore and in the urban areas of China. Dramatic changes in lifestyle in such regions brought about by growing economies, increasing affluence, and increases in the proportion of women in the industrial workforce have affected the population distribution of established breast cancer risk factors, including age at menarche and fertility and nutritional status, including height and weight. These changes have resulted in a convergence toward the risk-factor profile of Western countries.
What Happens If You Find Out Youre At Higher Risk
If you and your doctor determine that youre at a higher risk of breast cancer, you can decide together on next steps. Routine breast cancer screening is important for all women, but even more so for those at higher risk, so your doctor may suggest you get screened earlier and more often than other women.
You can also talk to your doctor about options for reducing your risk. Depending on your unique situation, your doctor may recommend either of the following:
- Risk-lowering drugs. Tamoxifen and raloxifene are the only drugs FDA-approved for breast cancer risk reduction in women at higher risk. Both are taken in pill form.
- Preventive surgery. For people with certain gene mutations, having surgery to remove their breasts may dramatically reduce their risk of breast cancer. Surgical removal of the ovaries can also reduce the risk of ovarian and possibly breast cancer for certain people.
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Racial And Ethnic Groups Within The United States And Studies Of Migrants
A detailed analysis of SEER data from 1975-2004 included 440,653 cases of breast cancer and showed a consistent finding of higher age-specific incidence of breast cancer among black women compared to white women younger than 40 years. After age 40 years, white women had higher incidence rates. This black-to-white incidence rate crossover was observed for all tumor characteristics and was consistent across birth cohorts. Black women have poorer 5-year survival rates from breast cancer at all ages of diagnosis compared to white women. This poorer survival can be attributed, in part, to the tendency of black women to be diagnosed at later stages of the disease.
According to a study from the American Cancer Society , in 2012, the breast cancer rates converged among black and white women even though white women have historically had higher incidence rates. Incidence rates were also significantly higher in black women compared with white women in seven states, primarily located in the South. However, more recent ACS data show a convergence of breast cancer rates among black and white women aged young than 65 years, a higher incidence in white women between ages 65 and 84 years, and then another convergence at age 85 years and older however, 2013-2017 data show higher death rates in black women regardless of age and across all racial and ethnic groups.
Breast Cancer: Risk Factors And Prevention
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ON THIS PAGE: You will find out more about the factors that increase the chance of developing breast cancer. Use the menu to see other pages.
A risk factor is anything that increases a persons chance of developing cancer. Although risk factors often influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. Knowing your risk factors and talking about them with your doctor may help you make more informed lifestyle and health care choices.
Most breast cancers are sporadic, meaning they develop from damage to a persons genes that occurs by chance after they are born. There is no risk of the person passing this gene on to their children, as the underlying cause of sporadic breast cancer is a combination of internal, or hormonal, exposures lifestyle factors environmental factors and normal physiology, such as DNA replication.
Inherited breast cancers are less common, making up 5% to 10% of cancers. Inherited breast cancer occurs when gene changes, called mutations or alterations, are passed down within a family from parent to child. Many of those mutations are in tumor suppressor genes, such as BRCA1, BRCA2, and PALB2. These genes normally keep cells from growing out of control and turning into cancer. But when these cells have a mutation, it can cause them to grow out of control.
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