Breast cancer usually starts in the inner lining of milk ducts or the lobules that supply them with milk. From there, it can spread to other parts of the body.
The exact cause remains unclear, but some risk factors make it more likely. Some of these are preventable.
The risk increases with age. At 20 years, the chance of developing breast cancer in the next decade is 0.6 percent. By the age of 70 years, this figure goes up to 3.84 percent.
If a close relative has or has had, breast cancer, the risk is higher.
Women who carry the BRCA1 and BRCA2 genes have a higher risk of developing breast cancer, ovarian cancer or both. These genes can be inherited. TP53 is another gene that is linked to a greater breast cancer risk.
- A history of breast cancer or breast lumps
Women who have had breast cancer before are more likely to have it again, compared with those who have no history of the disease.
Having some types of benign, or non-cancerous breast lumps increases the chance of developing cancer later on. Examples include atypical ductal hyperplasia or lobular carcinoma in situ.
- Dense breast tissue
Breast cancer is more likely to develop in higher density breast tissue.
- Estrogen exposure and breast-feeding
Being exposed to estrogen for a longer period appears to increase the risk of breast cancer.
This could be due to starting periods earlier or entering menopause later than average. Between these times, estrogen levels are higher.
Breast-feeding, especially for over 1 year, appears to reduce the chance of developing breast cancer, possibly because pregnancy followed by breastfeeding reduces exposure to estrogen.
- Body weight
Women who are overweight or have obesity after menopause may have a higher risk of developing breast cancer, possibly due to higher levels of estrogen. High sugar intake may also be a factor.
- Alcohol consumption
A higher rate of regular alcohol consumption appears to play a role. Studies have shown that women who consume more than 3 drinks a day have a 1.5 times higher risk.
- Radiation exposure
Undergoing radiation treatment for a cancer that is not breast cancer increases the risk of breast cancer later in life.
- Hormone treatments
- Occupational hazards
In 2012, researchers concluded that exposure to certain carcinogens and endocrine disruptors, for example in the workplace, could be linked to breast cancer.
In 2007, scientists suggested that working night shifts could increase the risk of breast cancer, but more recent research concludes this is unlikely.
Cosmetic implants and breast cancer survival
Women with cosmetic breast implants who are diagnosed with breast cancer have a higher risk of dying from the disease and a 25 percent higher chance of being diagnosed at a later stage, compared with women without implants.
This could be due to due to the implants masking cancer during screening, or because the implants bring about changes in breast tissue. More research is needed