Strategies to reduce breast cancer risk
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 . 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 .
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 .
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 .
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) , and for New Zealand women aged 45 to 69 years through BreastScreen Aotearoa .
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% .
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-) .
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 .
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
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 .
Breast cancer is rare in men, representing less than 1% of all breast cancer cases .
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 .
Risk factors you can change:
The risk of breast cancer associated with body mass index (BMI) differs by menopausal status.
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 .
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 .
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 .
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) .
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 . 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 .
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].
The relationship with parity (number of babies delivered) and breastfeeding, however, varies with breast cancer receptor status.
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 .
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 .
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 .
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
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 .
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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