A cost-effective study will be performed. The costs likely to differ between the two arms (MRI, biopsy, outpatient visits, hospitalisations, transportation, and sick leaves) will be assessed using data collected in the trial. The endpoint of the cost-effectiveness study will be the cost by success (cost-effectiveness ratio). A success is defined as achieving margin-negative resection after initial surgery (no need for re-excision). The other secondary endpoints will be to determine the rate of initial mastectomy and to describe MRI morphologic features in the MRI+biopsy arm.