Breast Cancer Incidence & Risk Factors

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Breast cancer is the second most common cancer and second leading cause of cancer death among women worldwide. In 2008 in Europe, 420, 000 women were diagnosed with breast cancer with a further 129, 000 estimated deaths from this disease. Breast cancer incidence and mortality varies significantly globally with a higher incidence rate found within developed counties. However through intensified detection efforts and the introduction of screening programmes mortality rates are now decreasing within high risk countries through the early diagnosis of smaller tumours.

Risk Factors

To date, several breast cancer risk factors have been well-established and include: age, ethnicity, cumulative exposure to hormones, body mass index, dietary factors, and family history of the disease. However, despite the establishment of well-defined breast cancer risk factors, it still remains difficult to initiate strategies for breast cancer prevention. Indeed, several risk factors display extreme difficulty in targetting, including family history and early onset of menarche (first menstrual cycle), however other factors appear easier to target and may also be important for reducing risk of other chronic diseases.

Easier to Target Risk Factors

  • Cumulative Exposure to Hormones

High levels of internal steroid hormones (including oestrogens and progesterones) in postmenopausal women are well-defined breast cancer risk factors. Oestrogens stimulate the growth of breast cells, therefore it has been postulated that enhanced cell growth may increase the accumulation of mutations in breast cells which lead to the development of cancerous cells. Therefore prolonged exposure to oestrogens may accelerate breast cancer development. Factors that increase lifetime exposure to hormones include: early menarche, regular ovulation, late menopause, nulliparity (not bearing offspring) or late age at first birth, lack of/or short term breast feeding, dietary factors and alcohol consumption . In postmenopausal women, obesity and long-term use of hormone replacement therapy (HRT) are principle determinants of oestrogen exposure and increase risk of breast cancer development. However it is thought that the timing of exposure to hormones is crucial to the development of breast cancer. Exposure to high levels of oestrogens early in life increases the risk of breast cancer development however the reduction of these levels later in life (via oophorectomy (removal of ovaries), cessation of postmenopausal hormone treatment or the administration of anti-oestrogens) may rapidly reduce this risk.

  • Body Mass Index

Obesity (BMI >30 kg/m2) is associated with increased risk of breast cancer, particularly within postmenopausal women. The ovaries are the main source of oestrogen production within the body however at menopause the ovaries cease to produce oestrogen. The major source of oestrogen production in postmenopausal women is synthesised within adipose (fatty) tissues, therefore the higher amount of fatty tissues within the body leads to enhanced oestrogen production thus increasing the risk of breast cancer development.

  • Dietary Factors

Substantial evidence exists to potentiate a role for dietary factors with increased risk of breast cancer onset, however results remain inconclusive and controversial and several studies indicate differential risks between pre- and postmenopausal women. Indeed, many studies have shown a positive correlation between enhanced intake of saturated and unsaturated fats and breast cancer development. High levels of these fats are found within red meat and dairy products and these foods are also thought to contain hormones which may contribute to breast cancer development. Other research groups have suggested that alcohol consumption of a minimum of one drink per day may contribute to breast cancer development. Indeed, these studies suggest that alcohol intake increases the level of oestrogen within the body, possibly through the limitation of the liver to control the blood level of hormones. Conversely, studies have indicated that vegetable intake and related dietary factors may protect against breast cancer. Therefore a diet restricted in high saturated fats and alcohol intake and high in vegetables is recommended and may protect against breast cancer development.

  • Exercise

Some researchers suggest that physical activity may reduce the risk of breast cancer development however the results remain elusive. It is thought that exercise may delay menarche and modify bioavailable hormones in the body thus decreasing exposure to oestrogens. However the duration and intensity of physical activity required to acquire and maintain these benefits remains unclear.

  • Smoking

The contribution of smoking to breast cancer has long been debated however recent evidence has shown a correlation between long-term heavy smoking and enhanced risk of breast cancer development; with results suggesting that risk enhances with increased exposure. However additional studies are necessary to further elucidate the mechanistic role and contribution of smoking to breast cancer onset.

  • Stress and anxiety

Little evidence currently exists to suggest a correlation between stress and anxiety and risk of breast cancer development. However, reducing stress levels contributes to enhanced quality of life and some research suggests that practices including meditation, yoga and prayer may contribute to a strengthened immune system.

Conclusion

Through the identification of well-defined breast cancer risk factors, intensified screening programmes are now widely available for patients with high risk of developing the disease, e.g. genetic predisposition, age and ethnicity. Although these programmes have significantly improved mortality rates within high risk countries through earlier detection and diagnosis of breast tumours, they cannot prevent disease occurrence. Therefore it is important to conduct easy-to-manage strategies to further prevent the risk of breast cancer development. Indeed, substantial and increasing evidence suggests that decreasing exposure to hormones and chemical toxins e.g. tobacco smoke, monitoring of weight and dietary intake and regular exercise may contribute to a decreased risk of breast cancer onset. Thus the employment of these strategies may not only aid in the prevention of breast cancer development however may also contribute to a strengthened immune system, overall health benefits and an enhanced quality of life.

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