What are the risk factors for breast cancer?

The development of breast cancer may be sporadic, familial or hereditary. Sporadic breast cancer means breast cancer that is not due to an inherited gene mutation, hence not hereditary. There are multiple risk factors responsible for sporadic breast cancer such as hormonal factors, dietary, lifestyle induced, benign breast diseases and environmental risk factors.

Majority of breast cancers are sporadic (approximately 70%), while 20-25% are familial and only 5-10% are hereditary breast cancer. In hereditary breast cancer, there is a mutated gene like BRCA which leads to breast cancer. In familial breast cancer there is no obvious mutation in genes but still other family members are at higher risk of developing breast or other cancers. Some of these risk factor can be modified, and their presence indicates a necessity of constant screening or active surveillance.

Non-modifiable risk factors: Risks due to genetic predisposition

Being a woman

Apart from stating what is (almost) obvious, being a woman is the biggest risk factor for breast cancer. Women have 100 times higher risk of developing breast cancer as compared to men. Male breast cancer contribution is less than 1% of total breast cancer burden.

Being an older woman

Women aged above 50 are at more risk to develop breast cancer as compared to younger women. This risk is considered to be the highest for women in their 70s. In last one decade because of the change in lifestyle and environment, the number of young breast cancer are increasing.

Family history

Breast cancer (and the genetic mutations responsible for the disease) can be passed on within a family. Having a close blood relative with confirmed breast cancer increases the risk of developing the disease, especially in later years. A woman is considered to be at 2X risk of developing breast cancer if a direct female blood relative such as her mother, sister (or even daughter) is diagnosed positive. If a woman has two or more first-degree relatives with breast cancer, her risk of developing the disease increases threefold. Up to 10% of all cases of breast cancer are hereditary.

Personal history of having breast cancer

Patients having a prior history of breast cancer are at a higher risk of developing contralateral breast cancer (in opposite breast), or in the different quadrant of the same breast if the patient had underwent breast conservative surgery.

Genetic abnormalities

Hereditary breast cancer constitutes 5-10% of all breast cancer. The most common genetic mutations occur in the BRCA1 and BRCA2 genes. Women with mutated BRCA1 gene have 60-85% lifetime risk of developing breast cancer while BRCA2 mutated patients have 40-60 % lifetime risk. BRCA mutated patients also have 20-30% lifetime risk of ovarian cancer. There are other genes like p53, PTEN, ATM which can lead to hereditary breast cancer.

Race and ethnicity

Breast cancer risk is also observed as a direct function of the patient’s race. For example, white (Caucasian) women are at a greater risk of developing breast cancer as compared to Asian, African-American or Hispanic women. Survival outcomes also vary according to race. For example, the probability of breast cancer related death is higher in African American women and Hispanic women, as compared to Caucasian women. Also, African-American women are most likely to develop an aggressive form of breast cancer at a much younger age as compared to women of other races and ethnicities.

History of menstrual activity

Early menarche and late menopause are important risk factors for breast cancer i.e. women who attained puberty before the age of 12 (with early menstrual activity) and women who attain menopause after the age of 55 are at a greater risk of developing breast cancer in their lifetime. This is attributed to a longer exposure towards estrogen, which stimulates the growth of cells within breast tissues. Similarly, exposure to hormone replacement therapies(HRT) after menopause can also boost a woman’s breast cancer risk.

Dense breasts

Mammographic breast density is an important risk factor. Patients with high breast density are at 2-4 times higher risk of developing breast cancer. Having dense breasts also makes it harder to mammograms to make an early detection of cancerous lesion in the breast tissue.

Previous breast changes/breast abnormalities

If any of the following conditions is present, a woman is considered to be at greater risk of developing breast cancer:

  • A personal history of benign breast lumps
  • A personal history of breast lumps
  • A personal history of breast cancer
  • A personal history of benign breast disease

Modifiable risk factors: Risks due to lifestyle habits and environmental exposure

Lack of physical activity

People with low or no physical activity are at an increased risk of developing breast cancer. Research has shown that 4 to 7 hours of moderate-to-intense exercise every week, can greatly reduce breast cancer risk.

Being overweight/obese

Women who continue to remain overweight/obese after menopause are more likely to develop breast cancer. This risk is commonly attributed to estrogen secretion by fat cells, after the age of menopause. In addition, being overweight also increases the levels of insulin present in blood, which in turn boosts a woman’s breast cancer risk. Women who have successfully completed breast cancer treatment are also at a higher risk of recurrence if they continue to remain overweight.

Alcohol consumption

Studies have shown that women who consume two or more alcoholic beverages in a day are at a 1.5 times higher risk of developing breast cancer as compared to women who do not consume alcohol. This risk is seen to increase with greater proportions of daily alcohol intake. Both the American Cancer Society (ACS) and the American Institute of Cancer Research (AICR) now recommend that women restrict their alcohol intake to one drink (30ml) per day.


Smoking is directly linked to a high risk of breast cancer among young and pre-menopausal women. Research has also demonstrated the links between heavy second-hand smoke exposure and breast cancer risk in postmenopausal women.

Exposure to radiation (before the age of 30)

Women who have been exposed to prolonged chest radiation at early age are at an increased risk of developing breast cancer later in their life. Women who have received radiation to the chest to treat any type of cancer other than breast cancer (such as Hodgkin’s lymphoma, non-Hodgkin’s lymphoma, chest wall sarcoma) are also at a higher risk of developing breast cancer than those who have not received radiation therapy.

Pregnancy timelines

Women who do not get pregnant at all (Nulliparous), or get pregnant after the age of 30 are at an increased risk of developing breast cancer. Women who did not complete a full time pregnancy are also at a higher risk of developing breast cancer.

Breast Feeding history

Women who have breast-fed their babies for one year or more, are at a lower risk of developing breast cancer as compared to those who have not.

History of Hormone Replacement Therapy (HRT)

Hormone Replacement Therapy (HRT) refers to the treatment used to relieve women from symptoms of menopause. HRT replaces hormones that are at a lower level, as women approach menopause. Women who are currently receiving HRT or have received it in the near past, have a higher risk of developing breast cancer.

Emerging risk factors

Vitamin D deficiency

Women with low levels of vitamin D are at an increased risk of developing aggressive/invasive forms of breast cancer. This is because vitamin D plays an important role in controlling the normal growth rate of breast cells, and may be able to stop breast cancer cells from growing.

Exposure to artificial light at night

Survey results have shown that women who work in night shifts, including doctors, nurses, and police officers, are at a higher risk of developing breast cancer compared to women who work during daylight. This is attributed to their increased exposure to artificial light at night. Women who live in areas with high levels of artificial external light during night (e.g. street light) also face a higher breast cancer risk.

Eating junk/unhealthy food

Unhealthy dietary habits are considered to be partly responsible for breast cancer. Whole foods and foods rich in antioxidants can boost human immune activity, and reduce the risk of breast cancer.

Eating processed foods/chemically preserved foods

Chemical food preservatives and enhancers include pesticides, antibiotics, and hormones that are used on both crops and livestock. Research has shown that these can contribute to increase in breast cancer risk. The risk extends to mercury found in seafood and industrial chemicals used in food and food packaging.

Eating grilled meat

Research has shown that women who eat a lot of grilled, barbecued, or smoked meats are at a higher risk of breast cancer as compared to those who have a diet consisting largely of fruits and vegetables.

Heavy use of cosmetics

Recent research has suggested that exposure to certain chemicals found in cosmetics, can contribute to the development and growth of breast cancer.

Excessive use of sunscreen

The use of sunscreen is intended to protect us against UV rays. However, recent research suggest that at excessive levels of exposure to some of the chemicals that are part of sunscreen creams can lead to breast cancer.

High exposure to plastic

Research has suggested, that at certain exposure levels, some of the chemicals used in manufacturing plastic products, such as bisphenol A (BPA), may act as carcinogens and boost breast cancer risk.

Exposure to chemicals in gardening products

There is strong research-backed evidence to support the theory that chemicals used in lawn and garden products may boost cancer risk. And while it is difficult to establish definitive cause and effect for any specific chemical, it is advised that women control their exposure to such substances in order to stay safe.

Drinking contaminated water

More than 206 drinking water contaminants have been identified till date. Although no conclusive evidence has been found relating these pollutants directly with breast cancer, some of these contaminants (such as chlorine and fluoride) are regulated by government bodies.

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