Breast cancer is the most common type of cancer in the UK; 1 in 7 women will develop it during their lifetime. Breast cancer forms when abnormal cells grow and multiply out of control within the breast. It is much more common in women, however, men can also develop breast cancer. The risk of developing breast cancer varies depending on factors including age, genetics, and lifestyle.
Obesity and smoking are two of the biggest lifestyle factors that increase the risk of breast cancer.1 As body weight increases, the risk of developing breast cancer after menopause also proportionally increases. Obesity is responsible for approximately 2-3% of cases and can increase the risk of developing postmenopausal breast cancer by 30%. Therefore, it is important to maintain a healthy weight throughout your life to reduce this risk.2,3
There are many types of breast cancer with the most common being invasive ductal carcinoma. Treatment and prognosis vary depending on the type diagnosed. Most types are split into two categories: invasive or non-invasive (or in situ). Invasive has the potential to spread to other parts of the body (metastasise) and may need more aggressive treatment to prevent this from happening.
Non-invasive is localised to the breast. Ductal carcinoma in situ (DCIS) is the most common type of non-invasive breast cancer and is an early form of the disease. Treatment often involves surgery and the prognosis is usually good if found before it develops the ability to become invasive.4
Once a biopsy of the mass has been taken, pathologists will examine the sample under the microscope to determine which type of breast cancer it is. In addition, further tests are performed to determine which proteins are on the surface of the cells. This tells the clinician which hormone receptors are present or absent. Tumours are classified depending on the following hormonal status:
It is important to determine the hormonal status as this influences the treatment options available. Hormonal therapies are typically effective in patients with ER+ tumours because they block estrogen receptors, thereby preventing estrogen from promoting tumour growth.
Conversely, drugs that specifically target HER2 receptors are effective in HER2+ tumours by blocking these receptors and inhibiting tumour growth. Triple-negative breast cancer is more common in younger patients and the treatment options are more limited, often involving chemotherapy.5
Obesity is a common risk factor for the development of 13 cancers including breast cancer. Overweight women after their menopause are at an increased risk of breast cancer. This also applies to men - the higher the body weight the higher the risk.6 Not only does obesity increase the risks for postmenopausal women, but being overweight at the time of diagnosis (at any age) results in a poorer prognosis. Therefore, it is important to understand the link between obesity and breast cancer.
Increased levels of oestrogen in postmenopausal women increases the likelihood of breast cancer development. It has been found women with postmenopausal breast cancer have 15% higher levels of oestrogen when compared to women without breast cancer.7 Oestrogen is one of the sex hormones normally produced from the ovaries in premenopausal women.
Oestrogen regulates many biological processes within the body including energy metabolism, the stress response, mineral balance, and sexual development. After menopause ovarian oestrogen decreases significantly. High levels of oestrogen are associated with an increased risk of ER+ breast cancer however, paradoxically these are more common in postmenopausal women.
Adipose tissue (fat) is one of the main sources of oestrogen post-menopause. The proliferative effects of oestrogen stimulate cancer growth and development within the breast tissue.8
In addition to the production of oestrogen from adipose tissue, fat cells express the enzyme aromatase. This enzyme is vital during the production of oestrogen from the hormone androgen. Therefore the more fat cells the higher the expression of aromatase, oestrogen levels increase, and the risk of breast cancer increases.8 Aromatase inhibitors are often used in ER+ cancers to reduce oestrogen levels.
Other mechanisms also contribute to the increased risk of breast cancer with obesity. Excessive adipose tissue results in adipocyte death, this releases molecules which attract immune cells and trigger an inflammatory state. This contributes to local and systemic chronic inflammation. The higher the levels of inflammation the greater the risk of cancer development.9
Obesity is also a known risk factor for the development of type 2 diabetes as a result of insulin resistance due to sustained high blood glucose levels. As well as regulating blood sugar levels insulin plays an important role in many other biological processes associated with cancer development such as tissue inflammation, motility, and angiogenesis (blood vessel formation). High insulin levels can promote aggressive cancer formation.10
The best way to reduce the risk of breast cancer associated with obesity is to maintain a healthy weight for your height throughout your life. This can be done by a combination of dietary management and physical activity. By preventing obesity and excess weight you will also be reducing your chances of developing many other illnesses including type 2 diabetes, heart disease, and cancers. Before undertaking any diets or changes to physical activity levels it is advisable to discuss this with a healthcare professional.
Eating a variety of different foods to ensure you are getting the right nutrients is vital to maintain a healthy weight. This should include foods from different classes including proteins, carbohydrates, fruits, and vegetables. Regularly cooking fresh foods rather than eating pre-prepared processed meals will also increase the nutritional value. Steaming or boiling food rather than frying is another healthier method of cooking. Sticking to a diet can be difficult so it's important to maintain variety to increase your chances of successfully losing and maintaining weight.3
Taking part in just 4-7 hours of exercise each week can reduce the risk of breast cancer by around 20%. This is because exercise lowers the levels of various hormones in the blood and reduces inflammation. This is especially important for women who have reached their menopause. Physical activity is also great for improving mental health. Currently, the NHS guidelines recommend 150 minutes of moderate exercise every week however, the more you can do the better!11
Treatment for breast cancer can involve surgery, hormonal treatments, chemotherapy, and radiotherapy. Increased weight has also been associated with poorer overall breast cancer survival which may be up to an 11% decrease in survival when compared to patients with healthy weights.
The risk of complications following surgery, chemotherapy, and radiotherapy increases with obesity and the risk of the cancer returning is also greater. Chemotherapy and hormonal therapies are also less effective partly due to obesity-related drug resistance to hormonal treatments.12
Breast cancer is common in the UK and obesity is a significant risk factor in the development of the disease. Obesity results in large deposits of fat which via a variety of mechanisms including oestrogen and aromatase production, chronic inflammation, immune modulation, and insulin resistance increase the chances of breast cancer development, particularly in postmenopausal women and men.
Obesity is also associated with poorer treatment outcomes and overall survival. By maintaining a healthy body weight and lifestyle by eating a balanced varied diet and staying active throughout adulthood it is possible to reduce this risk.
