usually, after lumpectomy, radiation to the breast and armpit are done. this will kill rogue cancer cells in the local area.
usually, (and especially when lymph nodes are positive), chemotherapy is also done to kill any possible rogue cancer cells that escaped to your body.
radiation and chemotherapy may or may not kill 100% of the cancer cells.
usually when lymph nodes are negative and the tumor is less than 4 cm in size, just a lumpectomy is needed. usually when lymph node(s) are positive, a modified radical mastectomy is preferred. this is because if the cancer cells were able to get from the tumor to the lymph nodes, they had to go through the breast lymphatics to get there, and some "in-transit" cancer cells may still be in the breast.
radiation and chemo may kill them, but surgical removal is more of a sure bet which is why modified radical mastectomy is usually preferred. it might be worth talking to the surgeon and asking him. there might be factors i am not aware of.
in any case, your wounds need to fully heal before chemo and radiation begin. open wounds that are given radiation or chemotherapy won't close, the wound stays open and gets infected.
statistics for survival of breast cancer are good and getting better every day with newer and better treatments. for a small, low grade cancer that has only spread to a few nodes, 10 year survival on the order of 75% or better.
here are some statistics:
http://www.cancerhelp.org.uk/help/default.asp?page=3317#larg other opinions and suggestions welcome!