Lifetime risks for breast cancer development
Most of us have heard the infamous statistic that …
… the risk factor for developing breast cancer is 1 in 8.
This statistic is interpreted by most women as 1 in every 8 women will develop breast cancer. However, this figure is slightly misleading and here is why …
Firstly, this statistic, 1 in 8, is what is known as an ‘absolute risk’. The absolute risk measures your risk of developing a particular disease over a certain time period. The absolute risk can also be expressed as a percentage or a decimal. So, for example, take an absolute risk of 1 in 30 for developing a disease in your lifetime, this can also be expressed as a 30% risk or a 0.3 risk.
It is ‘the over a certain time period‘ that is a very important factor. For instance, a 30 year old American woman does NOT have a 1 in 8 chance of developing breast cancer. In fact, the risk of breast cancer is 1 in 227 at the age of 30.
Furthermore, each individual woman’s risk of breast cancer is dependent on many factors both biological and environmental.
The Importance of Age and the Lifetime Risk of Breast Cancer
In 1989, a woman’s lifetime risk for developing breast cancer was about 1 in 10. That risk increased to about 1 in 7 by 2003 and is currently 1 in 8 in the US over an 80 year lifespan.
Even though it may seem that breast cancer risk has increased in recent years, the actual risk of dying from breast cancer has decreased significantly.
As we can see from the graph above, the likelihood of being diagnosed with breast cancer increases as a woman ages.
The percentages on the graph can also be translated to the following risk of breast cancer listed below:-
- Age 30: 1 in 227
- At age 40: 1 in 68
- Age 50: 1 in 42
- Age 60: 1 in 28
- At Age 70: 1 in 26
What jumps out at you from the above table is the exponential increase in probability between age 30 and 40 years.
A woman is around 3.5 times more likely to get breast cancer at age 40 than she was aged 30. In addition, between the ages of 40 and 50 there is another increase in probability.
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 woman’s 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.
Let’s take a look …
Risk of Breast Cancer: Factors that you can NOT control
Family History of Breast Cancer is a risk factor
There is an increased risk of breast cancer if a family relative has had breast cancer. Indeed, if a first-degree relative, that is a parent, sibling or child, has had breast cancer the risk is twice as high compared to women with no affected relatives.
If a woman has two affected first-degree relatives the risk of breast cancer is three times higher. For those women with three affected first-degree relatives the risk quadruples.
Age of Relative at diagnosis
The age of the affected relative at diagnosis also has an effect on the risk factor of breast cancer. A younger age at breast cancer diagnosis of a family member is associated with an increased risk for first-degree relatives.
The risk factor of breast cancer decreases as the age of the first-degree relative at diagnosis increases.
So, for example, if the relative was diagnosed before they are 40 years old the breast cancer risk is three times higher. If the relative was 40 to 50 years of age at diagnosis the unaffected relative has twice the risk. This decreases to 1.5 times more likely if the first-degree relative was between 50 and 60 at diagnosis.
Furthermore, there is no or little increased risk if the relative is diagnosed after 65 years of age.
Genetic Risk Factors for Breast Cancer.
Familial factors are slightly different from genetic factors. This is because lifestyle factors, such as obesity and diet are often shared in families.
Hereditary genetic factors, or gene defects, are in fact quite rare affecting around 5% to 10% of all breast cancer cases.
BRCA1 and BRCA2 Gene Mutations
The two most common major breast cancer predisposition genes are called BRCA1 and BRCA2. In inherited cases of breast cancer there is a mutation in these genes that creates a higher risk of breast cancer.
BRCA gene mutations only affect less than 1% of the general population although there are other rarer gene mutations too.
However, as you can see from our bar chart above, the risk of breast cancer with BRCA1 gene affected can be up to 87%.
However, the average risk according to the National Cancer Institute is around 55% to 65% of developing breast cancer by the age of 70 years. BRCA 2 mutations carry a lower risk of about 45%.
read on …
Dense Breast Tissue and Increased risk of Breast Cancer
For a woman, having dense breasts is associated with a higher risk of breast cancer. Only age and BRCA gene status carry a higher risk than dense breast tissue according to a 2015 medical study.
The ‘density’ of your breast tissue shows up on mammogram. Basically, dense breast tissue is made up of more glandular and fibrous tissue than fatty tissue. The dense breast tissue shows up as white on mammograms, like that of tumors.
The amount of breast density is expressed by the radiographer as a percentage. For women under 56 years with breast cancer, having a breast density of over 50% was three times more likely than in older women.
The risks for breast cancer in women with over 50% of dense breast tissue was 26%.
Recent medical studies have suggested that high percent mammographic density may be an inherited quality. However, breast density is also affected by age, certain drugs, pregnancy and menopause but can be changed. Furthermore, dense breast tissue makes screening less accurate.
According to the American Cancer Society, in general, higher percent breast density has an increased risk of 1.2 to 2 times that of women with average breast density.
Race and Ethnicity and Breast Cancer Risk
The risk of breast cancer incidence and mortality does vary according to different ethnic and racial groups. We can see the risk for each different racial group on our bar chart above.
In general, white women are more likely to develop breast cancer. However, there are many factors involved in breast cancer risk factors and race.
We have a whole new post on Incidence and Mortality Rates by Race.
Some Benign Breast Diseases increase the Risk of Breast Cancer
Although most women breathe a huge sigh of relief when diagnosed with a benign breast condition, some can lead to a slightly higher risk of breast cancer.
In general, there are 3 types of benign, or non-cancerous conditions of the breast:-
- Non-proliferative lesions
- Proliferative lesion without cell abnormalities (atypia)
- Proliferative lesions with cell abnormalites (atypia)
For non-proliferative lesions there is no, or a very slight increase in breast cancer risk. The second group of proliferative lesions, that do not show cell abnormalities, indicate a slightly increased risk of breast cancer.
However, the third group that includes atypical ductal hyperplasia and atypical lobular hyperplasia increase the risk of breast cancer by 3.5 to 5 times according to the American Cancer Society.
However, a recent research study suggests that the risk of breast cancer in atypical hyperplasia is higher than previously thought.
This study shows an absolute risk of later breast cancer after:-
- 5 years is 5%
- 10 years is 13%
- Over 25 years is 30%.
Carcinoma in-situ and Increased Risk of Breast Cancer
Carcinoma in-situ is a condition whereby abnormal cells of differing grades are present but do NOT break through the walls.
There are 2 main types of Carcinoma-in-situ
- Ductal Carcinoma in-situ (DCIS): The abnormal cells are present in the breast milk ducts
- Lobular Carcinoma in-situ (LCIS): The abnormal cells are present in the breast milk lobules
In general, predicting which cases of carcinoma in-situ will progress to invasive cancer is complicated with many inter-linked factors.
Both DCIS and LCIS carry a higher risk for invasive breast cancer. Most recurrences of breast cancer occur 5 to 10 years following a DCIS diagnosis. The chance of DCIS progressing to invasive breast cancer is under 30%.
However, according to a large research study based on SEER statistics, the incidence rate of invasive cancer for DCIS patients was 5.4/1000 person-years for (same side) breast cancer. For invasive breast cancer in the opposite breast, the rate of invasive cancer was 4.5/1,000 person-years.
The incidence of invasive cancer for LCIS patients is 5.3 times higher than DCIS patients. The lifetime risk of LCIS developing into breast cancer is estimated to be between 21% and 40%.
Hormones: Menarche and Menopause
The age at which a young girl starts her periods (menarche) and the age of menopause can both affect the risk of breast cancer.
A 2012 collaborative study found that breast cancer risk increased by 1.050 (or 5%) for every year younger at menarche. The risk for every year older at menopause was less at 1.029.
In general, younger age of menarche and older age at menopause increases the risk of breast cancer due to prolonged hormone exposure.
Old tables with (older) Data from the original Post
|Women’s Age||Risk of breast cancer|
|30||1 in 2000|
|40||1 in 233|
|50||1 in 53|
|60||1 in 22|
|70||1 in 13|
|80||1 in 9|
|overall||1 in 8|
|Women’s Age||Caucasion||Afrrican American||Asian/Pacific Islander||Hispanic|
|50-55||1.3%||1 in 75||0.8%||1 in 133|
|50-60||2.9%||1 in 34||2.3%||1 in 43||2.0%||1 in 51||1.6%||1 in 63|
|50-70||6.6%||1 in 15||5.0%||1 in 20||3.9%||1 in 26||3.7%||1 in 27|
Relative risk of breast cancer is increased with family history
As a general trend, if there is family history of breast cancer a woman’s relative risk for breast cancer increases to about 2.5. However, within the category of family history there are many associated sub-categories of risk including age of the family member.
|Age of relative with breast cancer history||relative risk of breast cancer|
- Altekruse SF, Kosary CL, Krapcho M, et al, SEER Cancer Statistics Review, 1975-2007. Bethesda, MD: National Cancer Institute; 2010 (Retrieved 02 April 2017) https://seer.cancer.gov/archive/csr/1975_2007/
- Howlader N, Noone AM, Krapcho M, et al (eds) SEER Cancer Statistics Review, 1975-2010, National Cancer Institute. Bethesda, MD,. http://seer.cancer.gov/csr/1975_2010/