What causes breast cancer in young women?

Possibly genetic: Breast cancer in younger women has a higher likelihood to be due to genetic abnormailties (so called brca1 and brca2 mutation). There are also many other familial or genetic abnormalities that are rarer. Many of the causes are still unknown. Check the following web page of myriad laboratory. It has a lot of useful information. https://www.myriad.com/ you may also check american cancer society's.

I wish we knew!: We don't know what causes breast cancer, and the rate in young women is increasing. We do know that a long exposure to estrogen increases your risk. If you started your period early, or never got pregnant, you have more estrogen exposure. Alcohol intake is associated with breast cancer. Any there are chemicals in our environment that are similar to estrogen, like bpa plastics. I suspect this!