Strategies to reduce breast cancer risk

Wellness Factsheet

Breast cancer most commonly begins when cells lining the breast lobules (milk-producing glands) or ducts (tubes that carry milk from the glands to the nipple) grow at an abnormal and uncontrollable rate. Breast cancer can then spread to other parts of the body, most commonly to the bone, and also brain, lung and liver depending on the breast cancer subtype [1]. It is worth knowing that breast cancer is not limited to women, however it is uncommon in men.

Did you know?

For the first time in two decades, female breast cancer has surpassed lung cancer as the most commonly diagnosed cancer worldwide, representing about 12% of all new cases of cancer [2]

In Australia, breast cancer is the most commonly diagnosed cancer among women, accounting for 29% of all cancers, and is second only to lung cancer in cancer deaths. The number of new cases for 2020 is estimated to have increased almost 270% since 1982 [3]

In New Zealand, breast cancer is the most common cancer in women, affecting 1 in 9 women during their lifetime. It is the third most common cancer overall [4].  

Breast cancer screening is encouraged every two years for Australian women over 40 years through BreastScreen Australia (though women aged 50-74 years are specifically targeted) [5], and for New Zealand women aged 45 to 69 years through BreastScreen Aotearoa [6].  

In 2017-2018, more than 1.8 million Australian women aged 50–74 years had a mammogram, representing only 55% of the targeted age group; in New Zealand, coverage was 70% [5]

The Facts

Most breast cancers are hormone sensitive. In these breast cancers, cells of the breast have receptors that can bind the hormones oestrogen and progesterone. This causes changes in the expression of certain genes that stimulate cells to grow more than normal. 

Most breast cancers are oestrogen-sensitive (ER), and of these most are also progesterone-sensitive (PR) i.e. they have receptors for these hormones.  About 19-22% of breast cancers lack oestrogen and progesterone receptors (ER- and PR-) [7].

  • ER- and PR- breast cancers are more difficult to treat and women have poorer survival.
  • ER/PR- breast cancers are more common in younger women, patients with advanced disease, sub-Saharan and African American women, and women with the BRCA1 gene [8].

Triple-negative breast cancers (TNBC) lack ER, PR and HER2 (a protein that promotes the growth of breast cells). About 10-15% of breast cancers are TNBC [7].

  • TNBC is an aggressive form of breast cancer with varied targeted therapeutic medications.
  • TNBC is more common in younger women (<40 years), African American and Hispanic women [8], women who harbour the BRCA mutation [9], and those that breastfed for shorter periods (<12 months) [8].

Breast cancer has well-established risk factors. Some can be changed, others cannot.  

Risk factors you cant change:

1. Inherited genetic mutations

The risk of developing breast and/or ovarian cancer is increased if a woman carries a harmful mutation in the BRCA1 or BRCA2 gene, but these are rare and only occur in less than 5-10% of either cancer [7,10]. 

2. Family history of breast cancer

  • Having one affected first-degree female relative (mother, sister, daughter) doubles the risk of breast cancer, while having two triples the risk [11]. 
  • However, 8 out of 9 women who develop breast cancer do not have any family links [5]. 

3. Age

Age is the greatest risk factor for breast cancer, with over three-quarters of breast cancer cases in Australia occurring in women over the age of 50 [5].

4. Gender

Breast cancer is rare in men, representing less than 1% of all breast cancer cases [5].

5. Eearlier menarche and later menopause

The risk of breast cancer may increase with longer periods of reproductive years. Early menarche (the first menstrual cycle occurs at 12 years or younger) and later menopause are both associated with increased risk [12].

  • Early menarche is somewhat modifiable, as childhood overweight contributes to early puberty in girls [13].

6. Nulliparity

  • Women who are over 70 years old and have never given birth have a higher risk of breast cancer than women who have given birth, especially if they are overweight [14].    

Risk factors you can change:

1. Obesity

The risk of breast cancer associated with body mass index (BMI) differs by menopausal status.

  • Postmenopausal women: A recent meta-analysis of more than 3 million women, showed that a higher BMI increased the risk of postmenopausal breast cancer by 33% (1.03 times higher for every BMI unit increase), particularly for ER+ breast cancer. No association was found with premenopausal women.[15]
  • Before menopause, oestrogen is made predominantly by the ovaries, but afterwards it is made by fat cells, also present in breast tissue.

2. Hormone replacement therapy (RPT)

A meta-analysis found a 60% increase in breast cancer for oestrogen-progesterone HRT used for less than 5 years compared to 17% for oestrogen only; with a twofold greater risk of breast cancer after 5-14 years use of dual HRT compared to 33% increased risk for oestrogen only. Daily use of the dual HRT increased the risk to 2.30-fold compared to 1.93 for less frequent use. No risk was found with the use of vaginal oestrogens [12].

3. Smoking

Smokers (including passive smokers) have a modestly increased risk of breast cancer [16-19], particularly if they started in adolescence, smoked for longer or smoked more cigarettes across their lifetime [19].

4. Alcohol

Alcohol use, even at low levels of three to six drinks per week, and binge drinking at moderate levels for those with a familial history, increases the risk of breast cancer [20-23].

5. Fat intake

A meta-analysis of cohort studies examining dietary fat and breast cancer mortality found a 50% greater risk of breast cancer death for women in the highest category of saturated fat consumption than those in the lowest category [24].

6. High red meat intake

Higher red meat intake, including fresh and processed meats, may be a risk factor for breast cancer. In the Sister Study of 42,000 women who were followed for an average of 7.6 years, the quarter who ate the most red meat (average of 53g daily) had a 23% greater risk of invasive breast cancer than those who ate the least (average of 7.4g) [25].

What can you do to decrease risk:

1. Increase fibre in your diet

A high fibre diet is associated with a reduced risk of breast cancer, with each additional 10 grams of fibre eaten per day associated with a 4% lower overall risk of breast cancer [26]. However, the earlier consumption occurs the greater the risk reduction.

2. Include flaxseeds in your diet

There is growing research on the potential of flax seeds to reduce breast cancer risk and tumour growth, largely due to its high lignan content. Lignans are antioxidant phytoestrogens with antioestrogen properties [27].

3. Breastfeeding and childbearing

Multiple studies have shown breastfeeding to have a protective effect, with the size of the effect dependent on how long breastfeeding had occurred and how many successful pregnancies (parity) there had been [7,28,29].

  • In a systematic review and meta-analysis, breastfeeding for more than 12 months was associated with a 26% reduction in the risk of breast cancer [29].

The relationship with parity (number of babies delivered) and breastfeeding, however, varies with breast cancer receptor status.

  • Pregnancy protects against ER+, the most common type of breast cancer [30]. 
  • In contrast, greater parity increases the risk of ER- breast cancer and significantly increases the risk of TBNC, but only if women never breastfed [31].

4. Eating fruits and vegetables

Studies have suggested a decreased breast cancer risk in diets high in fruit and vegetables, possibly due to high circulating levels of alpha-carotene, beta-carotene, and total carotenoids [32]. 

5. Soy consumption

Eating soy leads to a better prognosis and improved survival rates, with reduced risk of cancer recurrence and death - even for ER+ breast cancers - with the greatest benefits seen the earlier consumption was initiated [33,34].

6. Vitamin D levels

A large meta-analysis involving 11,656 women found that postmenopausal breast cancer risk decreased as circulating vitamin D levels increased to optimal levels, flattening at doses >35 ng/mL. No association was found for premenopausal women [35]. 

7. Regular physical activity

Regular physical exercise may offer some protection against breast cancer. A 2016 review estimated that the most physically active women had a 12-21% lower risk of breast cancer than the least active women [36].

What can we do about it

Maintain a healthy weight

Be physically active

Eat your fruit and vegetables

Reduce red meat intake

Eat a high fibre, low-fat diet

Limit alcohol

Quit smoking or never smoke

Keep your vitamin D levels within the normal range

Breastfeed your baby for as long as you are able

Schedule your free mammogram every two years if you are a woman aged between 50 and 74 (Australia) or between 45 and 69 (New Zealand). Even though mammograms do not prevent breast cancer, they have been shown to reduce cancer mortality by identifying breast cancer at an earlier stage [3].

Even though you can’t change some risk factors for breast cancer, there is still a lot you can do to reduce your risk.


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