Unfortunately, there's no definite answer here. It is believed to be a combination of both known and unknown factors like genetics, lifestyle, choices such as diet and alcohol use, and reproductive factors such as the age of your first period and menopause.
Most breast cancers are not genetic (inherited) in origin. However, if you have a close relative that has had breast cancer, let your doctor know so you can discuss the risks.
Although your chances of getting breast cancer at a younger age are low, cancers in young women tend to be more aggressive. So, you don't need to worry, but you should get to know your breasts well, check them regularly and report any unusual changes to a doctor.
There are simple things you can do like eating healthy, exercising and not drinking or smoking. Check our Prevention section for more information.
Young women's breasts are sometimes dense, making any early signs of cancer hard to see. Regularly looking and feeling for changes yourself is your best defense.