Survivor since 2012
It depends on so many factors: size of tumor, type of cancer, whether it's spread to your lymph nodes, and many more issues. I've had breast cancer twice. The first time, in 2000, I elected to have a mastectomy. They recommended radiation only, followed by 5 years of Tamoxifen and 3 years of Femara.
This time, because of the size of the tumor, I had a mastectomy and am just finishing up chemo. So it all depends. Your doctor will tell you about any options you may have. Best of luck!