What are the risks of breast cancer returning within a year of original treatment if taking tamoxifen?

Hopefully low: But highly dependent on your history, the type of breast cancer, size of tumor or if lymph nodes were involved, hormone receptor status, if radiation therapy was given, type of surgery, etc. Would need much more detailed information than can be answered here. Your medical oncologist would be the best resource to this question for your own specific situation.

Low: Most women do well if their tumor is removed and it is in early stages...With high cure rates of 80-85% for stages 1 and 2.. The chances of return within one year of orginal diagnosis have to be very low, perhaps about 5% in my view.