Breast cancer

I have a colleague who had undergone mastectomy and chemotherapy for breast cancer. She is 60 years old now and still looking good, hale and hearty. My brother's wife has the same plight, she gets a checkup every year to make sure that the cancer will not come back. I sometimes wonder why breast cancer had become prevalent in the last 3 decades. There were no cases I know of when I was younger. Is it because of the food or the lifestyle or the pollution?