Understanding What Causes Breast Cancer

Breast cancer is one of the most common forms of cancer amongst women. It is caused by mutations or damage to the DNA in breast cells. 

Certain factors can affect your likelihood of developing breast cancer. While some of these factors (age, family history, and dense breasts) are not in your control, others, like lifestyle factors, are. 

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We make it easy for you to participate in a clinical trial for Breast cancer, and get access to the latest treatments not yet widely available - and be a part of finding a cure.

Genetic factors

1. Age

While being a woman is the biggest risk factor for breast cancer, age is the second. The risk of developing breast cancer increases as you get older¹. Women over the age of 50 who have been through menopause are most at risk of developing breast cancer. They account for over 80% of cases. 

Women between 50 to 70 years of age are advised to be screened for breast cancer every two years. 

2. Family history

Some women inherit a gene mutation from either parent that puts them at a higher risk for breast cancer. About half of all breast cancer cases result from these hereditary gene mutations², usually from the BRCA1 or BRCA2 gene

Besides these genes, other mutations that can increase your risk of developing breast cancer include:

  • ATM

  • CHEK2

  • PALB2

  • TP53

  • PTEN

  • CDH1

  • STK11

3. Whether you’ve had breast cancer before

For those who have already had breast cancer, the risk of developing it in the other breast or a different part of the original breast is three to four times higher³ than those who have never had breast cancer.

Other changes in your breast tissue, such as abnormal growth of cells in ducts (typically ductal hyperplasia), or abnormal cells in your breast lobes (lobular carcinoma in situ), increase the risk of getting breast cancer. Various kinds of breast lumps may also increase your chances of developing cancer.

4. Dense breast tissue

The breasts are made up of thousands of tiny glands (called lobules) that produce milk. This glandular tissue has a higher concentration of breast cells than other breast tissue, making it denser. 

Women with dense breasts seem to have a higher chance of breast cancer since more cells can become cancerous⁴. It also affects diagnosis since dense breast tissue can hide lumps or abnormal tissue, making breast scans (called mammograms) challenging to read. 

Younger women tend to have denser breasts than older women. The amount of glandular tissue in your breasts reduces and is replaced with fat as you get older, meaning your breasts become less dense with age. 

5. Hormones 

The risk of developing breast cancer may increase with the amount of estrogen your body is exposed to. For example, women who begin having their periods at a young age or experience menopause later than average will be exposed to estrogen over a longer time. 

Not having children or having children later in life can also increase your risk of developing breast cancer. This is because your exposure to estrogen has not been diminished by pregnancy. 

6. Pregnancy 

Having children has a complicated effect on breast cancer risk. Women who have never given birth or have their first child after the age of 30 have a higher risk of breast cancer than women who gave birth before the age of 30.

Post-pregnancy, however, there is a short-term increased risk of breast cancer that reduces after ten years - why this happens, we are still trying to work out. 

7. Hormone replacement therapy medication

The relationship between hormone replacement therapy (HRT) and breast cancer is complex. Generally, all types of HRT - apart from vaginal estrogen - can raise the risk⁵ of breast cancer over time. 

Taking HRT for one year or less is associated with only a slight increase in breast cancer risk. However, the longer HRT is used, the greater the risk of breast cancer. In general, over time, the increased risk of breast cancer reduces to baseline after stopping HRT.

The risk of breast cancer due to HRT varies from person to person. Factors like when you started HRT, other medications being taken, and your overall health can impact breast cancer risk and should be discussed with your doctor. 

8. The contraceptive pill

Studies show that women who take the combined (both estrogen and progestogen) contraceptive pill have a slightly increased risk⁶ of developing breast cancer. This risk is greatest for those women aged 45 and over.

The risk, however, reduces once you stop taking the pill. The risk of developing breast cancer is back to baseline ten years after stopping. 

Lifestyle factors

1. Being overweight or obese

If you are considered overweight and have also gone through menopause, you may be more likely to develop breast cancer. 

Studies show that a five-unit increase in body mass index (BMI) in postmenopausal women results in a 12% increase⁷ in breast cancer risk. This is because fat cells produce estrogen, and increased exposure to estrogen increases the risk of breast cancer. 

2. Smoking

Smoking cigarettes and consuming nicotine products generally increase⁸ the risk of breast cancer. The risk is higher for those who start smoking at a younger age.

If you have a family history of breast cancer and are a smoker, this significantly increases your risk of breast cancer.

3. Drinking alcohol

Drinking even a relatively small amount of alcohol is related to an increased risk of breast cancer⁹. The more alcohol you drink, the higher the estrogen levels are in your body, and this increases your risk of developing breast cancer.

4. Diet

Some foods can increase your risk of breast cancer. These foods include: 

  • Fried food 

  • Processed meats like bacon, sausages, and cold cuts 

  • Sugary foods

  • Refined carbohydrates 

5. Radiation

Exposure to medical procedures that use radiation, like x-rays or CT scans, may increase your risk of developing breast cancer.  

Also, exposure to ionizing radiation can increase your chances of breast cancer. Ionizing radiation is any type of radiation with enough energy to change an atom, such as nuclear energy or x-rays. 

Results from studies¹⁰ of medical exposures to radiation as well as large-scale disasters like exposures from the atomic bomb in Japan have proven that radiation can cause breast cancer.

6. Environment

Different chemicals and toxins can mimic or imitate the effects of estrogen in the body, and exposure to them may increase your breast cancer risk. 

Examples include BPA (bisphenol A), DDT, and heavy chemicals including arsenic, mercury, lead, atrazine, and phthalates. 

What causes breast cancer in men? 

According to the CDC (Centers for Disease Control and Prevention), male breast cancer accounts for around one in every 100 breast cancer diagnoses.

Although it is rare, breast cancer in men does occur, and certain factors may increase the risk of it developing, including:

  • Inherited genetic mutations (BRCA1 & BRCA2)

  • Age

  • Being overweight

  • A family history of breast cancer

  • Previous history of radiation therapy

  • Previous history of hormone replacement therapy

  • High alcohol consumption

In addition, these conditions may contribute to a higher risk of breast cancer developing in men:

  • Conditions that affect the testicles

  • Liver disease

  • Klinefelter syndrome - a rare genetic disorder in which a male has an extra X chromosome. Klinefelter syndrome can lead to the body making higher levels of estrogen and lower levels of androgens (a hormone that develops and maintains male sex characteristics).


Not everything you’ve heard about breast cancer is true. Keep reading to understand why certain foods, behaviors, and factors won’t increase your risk of developing the disease. 


Rumors that using deodorants and antiperspirants increases your risk of breast cancer have been around for decades. However, there is no compelling evidence that there is a link between breast cancer and deodorants, antiperspirants, or their ingredients.


Despite several studies conducted over the years, there has been no conclusive evidence that breast cancer can be caused by stress. 

Having an abortion

Having an abortion does not increase your risk of developing breast cancer. 

Underwire bras 

There have been speculations that the wires in underwire bras may restrict the flow of lymph fluid, causing toxins to build up. However, there is no evidence to support this. 

Mobile phones

While some worry that radio waves produced, emitted, and received by mobile phones may be a health risk¹¹, there is no evidence that radiation from mobile phones affects your risk of developing breast cancer.

Nipple piercings

Currently, there is no evidence to support the claims that having a nipple piercing can affect your risk of getting breast cancer. 

Breast injury 

Injuring, squeezing, or falling on the breast area will not cause breast cancer. Neither will pinching the nipple or breast. These actions may cause swelling or bruising, which can be painful.

Other times, an injury on the breast can lead to a benign lump, known as fat necrosis. This scar tissue forms when the body naturally repairs the damaged fatty breast tissue. 

The lowdown

There are many possible causes of breast cancer, and not all women at risk will develop it. Factors such as exposure to natural substances, a genetic predisposition, hormone imbalances, and certain infections can all affect who develops breast cancer. Whether or not you develop the disease depends on these factors and factors within your own body.

Learn about steps you can take to manage your risk level and help reduce the likelihood of breast cancer developing.

Have you considered clinical trials for Breast cancer?

We make it easy for you to participate in a clinical trial for Breast cancer, and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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