The anti-estrogen medications such as Arimdex are published to be very effective in estrogen positive breast cancer keeping cancer at bay not only locally but elsewhere. I have read that there is a blood test available, given to early stage breast cancer patients that can determine which patients may or may not benefit from chemo. Studies indicate not everyone will respond to chemo despite their harsh side effects so it may or may not add any benefit. In the case of lumpectomy, they normally do radiation to eradicate any remaining cells still left in remaining breast tissue. I was given the option 4 years ago with my stage l to either have lumpectomy with radiation or a mastectomy. I have read, however, that radiation after mastectomy may give some additional benefit. I would hope that you still have your check ups with your team as there maybe residual breast tissue remaining even after mastectomy that can become cancerous so follow ups are crucial for this as well.