Risk factors of breast cancer

                                         Risk factors of breast cancer
The primary risk factors for breast cancer are female sex and older age. Other potential risk factors include: lack of childbearing or breastfeeding, higher hormone levels,diet and obesity.

Lifestyle

See also: List of breast carcinogenic substances

Smoking tobacco appears to increase the risk of breast cancer with the greater the amount of smoked and the earlier in life smoking began the higher the risk. In those who are long term smokers the risk is increased 35% to 50%. A lack of physical activity has been linked to ~10% of cases.
The association between breast feeding and breast cancer has not been clearly determined with some studies finding support for an association and others not. In the 1980s the abortion–breast cancer hypothesis posited that induced abortion increased the risk of developing breast cancer. This hypothesis has been the subject of extensive scientific inquiry which has concluded that neither miscarriages nor abortions are associated. There may be an association between oral contraceptives and the development of premenopausal breast cancer. Whether or not this association is causal is debated and if there is indeed a link the absolute effect is small. In those with BRCA1 or BRCA2 mutations or a family history modern OCPs do not appear to affect the subsequent risk of breast cancer.
There is a relationship between diet and breast cancer including an increased risk with a high fat diet, alcohol intake, and obesity. Dietary iodine deficiency may also play a role.
Other risk factors include radiation shift-work. A number of chemicals have also been linked including: polychlorinated biphenyls, polycyclic aromatic hydrocarbons, organic solvents and a number of pesticides. Although the radiation from mammography is a low dose, it is estimated that yearly screening from 40 to 80 years of age will cause ~225 cases of fatal breast cancer per million women screened.

Genetics

Some genetic susceptibility may play a minor role in most cases. Overall, however, genetics is believed to be the primary cause of 5–10% of all cases. In those with zero, one or two affected relatives, the risk of breast cancer before the age of 80 is 7.8%, 13.3%, and 21.1% with a subsequent mortality from the disease of 2.3%, 4.2%, and 7.6% respectively. In those with a first degree relative with the disease the risk of breast cancer between the age of 40 and 50 is double that of the general population.
In less than 5% of cases, genetics plays a more significant role by causing a hereditary breast–ovarian cancer syndrome. This includes those who carry the BRCA1 and BRCA2 gene mutation. These mutations account for up to 90% of the total genetic influence with a risk of breast cancer of 60–80% in those affected. Other significant mutations include: p53 (Li-Fraumeni syndrome), PTEN (Cowden syndrome), and STK11 (Peutz–Jeghers syndrome), CHEK2, ATM, BRIP1, and PALB2. In 2012, researchers said that there are four genetically distinct types of the breast cancer and that in each type, hallmark genetic changes lead to many cancers.

Medical conditions

Certain breast changes: atypical hyperplasia and lobular carcinoma in situ found in benign breast conditions such as fibrocystic breast changes are correlated with an increased breast cancer risk.