Breast Cancer Risk Factors
The most important risk factors for breast cancer are female sex and age. Women are 100 times more likely to get breast cancer than men. The risk increases with advancing age: 75 per cent of breast cancers occur after the age of 50.
Genetics play an important role in only 5-10 per cent of breast cancers. In other words, 90 per cent of the breast cancers are so called sporadic (by chance). Based on the number of affected first and second-degree relatives with breast or ovarian cancer, women are divided into three categories:
Average risk: 1 in 11 to 1 in 8 chance of breast cancer by the age of 75.
Moderate risk: 1 in 8 to 1 in 4 chance of breast cancer by age of 75.
High risk: More than 1 in 4 chance of breast cancer by age of 75.
If you have multiple family members with history of breast cancer specially at young age, or any relative with history of ovarian cancer, or breast cancer in a male relative it is important to see a breast specialist to go through your family history and determine your risk. This has practical implications to determine the intensity and modality of breast cancer screening in women as well as approaches to manage their risk. For example, screening for women at average risk of breast cancer is done by two yearly mammography through BreastScreen. If you are a woman who is at high risk of familial breast cancer, further assessment in a familial breast cancer clinic is warranted. This includes genetic assessment, annual screening often with breast MRI from as young as 25 years of age, and discussions about risk reducing surgery and medications.
Can I reduce my risk of breast cancer?
There are some ‘so called’ modifiable breast cancer risk factors such as obesity, alcohol use, high fat diet, and sedentary lifestyle. Although each one in isolation is considered a minor risk factor, presence of multiple of these risk factors together can add up to a substantially increased risk of breast cancer. Prolonged combined hormone replacement therapy (HRT) in postmenopausal women has been shown to increase risk of future hormone positive breast cancer and therefore risks and benefits of HRT should be considered on an individual basis. In women with high risk of familial breast cancer risk-reducing interventions may be discussed. The most effective risk-reducing strategy is bilateral mastectomy which reduces future risk of breast cancer by 90-95%. The other option is taking tamoxifen which reduces the risk by about 50%.
