Background: The locoregional lymph nodes were recognized not to work as the defense against to cancer cells spreading to the organs.The prognosis in approximately 60% of the breast cancer patients depends on the local treatment alone.The other 40% depends on the local and systemic treatments.Breast conserving therapy has been proved to be as good as mastectomy for breast cancer in several clinical trials.The aim of local treatment is to completely eradicate the cancer cells from the breast.MRI is the best modality in spatial resolution for the detection of breast cancer ductal spread.Two phase Ⅱ clinical studies (excision studies) to investigate pathological efficacy and clinical safety of MR guided focused ultrasound surgery (MRgFUS) were conducted and their outcome has been published.Purpose: To inspect the efficacy and safety of MRgFUS followed by radiotherapy in excisionless study.Methods: The inclusion criteria include 1) tumor diagnosed by needle biopsy under ultrasound 2) Receptor status of cancer cells confirmation 3) tumor size 15mm 4) well demarcated mass in contrast enhanced MRI.The exclusion criteria include 1) pure type mucinous carcinoma, 2) invasive micropapillary carcinoma 3)skin dimple or dimpling sign, previous surgical scar of the skin above the tumor, 4) location of the tumor requires a high sonication angle.Needle biopsy was performed again within three weeks after ablation and no residual viable cancer cells were identified by Hematoxylin-Eosin stain and single strand DNA immunohistochemical stain.The following radiotherapy is whole breast(50Gy) and boost(10Gy).Results: Fifty seven patients entered this study and forty-seven lesions were treated from April 2005 to December 2010.The median age was 58 years old (37-79).The average tumor size was 10.8mm (6-15).The median follow up period was 43 months (3-64).Thirty-four cases were followed up for more than 24 months.There were no severe adverse events, local and distant recurrence cases.Conclusions: Although the number of cases is still small and the follow-up period is short, MRgFUS has the potential of replacing usual breast conserving surgery.Strict selection of cases is essential.