Sample size
RECURRENCE
For sample size calculation, we estimated a difference in the local recurrence rate of 7% between conservative surgery and mastectomy as reported in the literature in twenty years of follow-up [Since by the time our trial was activated, there was no available evidence to estimate the impact of MRI on local recurrence after breast-conserving surgery, we used the mastectomy rate for sample size calculation. We hypothesized that MRI would increase the mastectomy rate due to the finding of additional foci and decrease local relapse. We used that hypothesis as a surrogate for our sample size calculation.