If you are "NED"; no evidence of disease you could be considered in remission.
Hi. If you have an early stage breast cancer confined to the breast alone with no involvement of distant organs, surgically removing the primary tumor will leave no obvious trace of disease. The effectiveness of any post-surgery treatment (called "adjuvant" treatment) like radiotherapy cannot be immediately assessed because there's nothing to observe. Unless new lesions are seen on repeat mammogram, in which case, there is clearly a failure of treatment. Adjuvant treatment can only be deemed effective if the cancer does not recur. This means that the patient has to be observed for a number of years (e.g. 10 years) for any sign of cancer recurrence. So its still too early to say if you are truly in remission, particularly since no repeat ultrasound or mammogram has been done yet.