Understanding Breast Cancer Risks

Breast Cancer Risks

What are the factors that may affect your risk of having breast cancer?

Some factors help increase the probability or having breast cancer and a selected few help lower risks. Some affect risk a great deal and others by only a small amount.

Although we’ve learned a lot, we still don’t know what causes breast cancer to develop at a certain time in a certain person. It’s likely a combination of risk factors (some of which are still unknown).

However, why a certain combination of factors might cause breast cancer in one person, but not in another, is still unclear. 

Types Of Cancer Risks

absolute Risks

Absolute risk


The most basic type of risk is absolute risk. Absolute risk is a person’s chance of developing a certain disease over a certain period of time.

Absolute risk is estimated by:

  • Looking at a large group of people who are similar in some way (the same age, for example) and
  • Counting how many people in the group develop a certain disease over a certain period of time

Knowing the absolute risk of a disease can help you understand the health risks in your life.

Example of 1-year absolute risks

If we followed 100,000 women ages 30-34 for one year, about 25 women would develop breast cancer [552].

So, the 1-year absolute risk of breast cancer for a 30-34 year-old woman is 25 per 100,000 women (or 1 per 4,000 women). This is risk is less than 1 percent.

Another way to say this is the chances of getting breast cancer in the next year are less than 1 percent for the average 30-34 year-old woman.

This example shows the 1-year absolute risk of breast cancer for a young woman is low.

Examples of 10-year absolute risks

You may see absolute risk presented over long periods of time.

The table below shows the 10-year absolute risks of breast cancer by age

are low in young women


Lifetime risks
Accumulate with age

One absolute risk you may see is lifetime risk of breast cancer.

American Women living in the U.S. have around 12% chance of getting breast cancer. This means that “1 out 8” women will receive a positive diagnosis for become breast cancer in their lifetime, therefore become breast cancer patients. [552].

an important factor regarding Lifetime risk of breast cancer is that this risk is cumulative.  Risks of getting breast cancer adds up all the 1-year absolute risks over the course of a woman’s life. 

So, it’s much higher than the 1- or 10-year absolute risks of breast cancer.

Lifetime risks
Accumulate with age


The projected number of new breast cancer cases for 2018 according to specialists and health care organizations forecasts are: be [50]:

 266,120 new cases of invasive breast cancer.

(This includes new cases of primary breast cancer, but not recurrences of original breast cancers.)

63,960 new cases of in situ breast cancer

In situ cases  include the following types of cancer”

  1.  Ductal carcinoma in situ (DCIS) and 
  2. Lobular carcinoma in situ (LCIS). 

from all cases, about 83 percent will be DCIS [51]. 

DCIS is a non-invasive breast cancer. LCIS is a condition that increases the risk of invasive breast cancer. Learn more about DCIS and LCIS.)

40,920 breast cancer deaths


Contrary to common belief, Breast Cancer occurs in men.

The number of case incidence in men is only a fraction compared to women. In fact, male breast cancer is rare, but it does happen.

The estimates for U.S. Male Breast Cancer cases In 2018, is estimated to be as follows [50]:

2,550 new cases of invasive breast cancer 

This estimation includes new cases of primary breast cancers, but not recurrences of original breast cancers.

480 breast cancer deaths

The rates of breast cancer incidence (new cases) and mortality (death) for the U.S.population are much lower among men than among women [52].



Breast Cancer Lifetime risks
varies worldwide

General risks Factors

Risk factors

Anything that increases or decreases a person’s absolute risk of getting a disease is called a risk factor.

A risk factor can be related to:

  • Lifestyle (such as exercise)
  • Reproduction (such as age at first period)
  • Genetics (such as family history)
  • The environment (such as radiation exposure)

Some factors increase risk.

For example, older women have a higher risk of breast cancer than younger women. So, age is a risk factor for breast cancer.

Some factors decrease risk.

For example, women who breastfeed have a lower risk of breast cancer than women who don’t. So, breastfeeding is also a risk factor for breast cancer.


Play Video

Age is An important risk factor:
Older Women (men) Have a Higher risk
Of Cancer Than Younger Women

relative risks

Relative risk

compares the risk of disease between two groups of people. It compares one group with a certain risk factor for a disease to another group’s risk. 

For instance, imagine you are comparing the risk of breast cancer among 2 groups of 100 women. But only the women in 1 group have a certain risk factor for breast cancer. The other group of women does not have this risk factor.

Researchers keep track of how many people from each group develop cancer over a certain time. Let’s say they find that 2 women who have the same risk factor get cancer. But only 1 woman without this risk factor gets cancer. Then those in the first group have 2 times the risk of the second group. This is a 100% increase in relative risk. The absolute risk, however, would be 2% or 2 out of 100 people.

Patients can use risk measurements to make better choices about lifestyle changes or cancer screening. It is also important to know the difference between absolute and relative risk. 

For instance, the relative risk in the last example might sound high. It identified a person’s relative risk of developing cancer by 100%. But look at the absolute risk to get a more complete picture. That is, 1 person in 100 compared to 2 people in 100. If you want to compare the research you hear about in the news to your own situation, make sure you find the absolute risk.

Most research studies report relative risks. This can make the risk sound higher than it actually is.

Example Of
relative risk


Say a study shows women who don’t exercise (inactive women) have a 25 percent increase in breast cancer risk compared to women who do exercise (active women).

This statistic is a relative risk (the relative risk is 1.25). It means inactive women are 25 percent more likely to develop breast cancer than women who exercise

A relative risk compares two absolute risks.

  • The numerator (the top number in a fraction) is the absolute risk among people with the risk factor.
  • The denominator (the bottom number) is the absolute risk among those without the risk factor.

The absolute risk of those with the factor divided by the absolute risk of those without the factor gives the relative risk.

"Women who breastfeed have a 6 percent lower risk of breast cancer compared to women who do not breastfeed."

Leading A Healthy Life

Making healthy choices

Understanding absolute risk and relative risk can help you make informed choices about your health.

No matter your risk of breast cancer, a healthy lifestyle is important.

Doctors From Memorial sloan Kettering
Breast cancer risks & Myths