The purpose of this prospective observational study is to evaluate the impact of preoperative breast MRI in patients with breast cancer selected for breast- conserving surgery. MRI is a more sensitive radiological modality than mammography and ultrasonography. Patients with small breast cancers are, based on conventional modalities, selected for breast-conserving surgery. If preoperative breast MRI reveal additional lesions in the breasts, and malignancy is confirmed histopathologically, this finding leads to a change of surgical method to mastectomy.

The aim of the study is to evaluate the impact of preoperative breast MRI on primary surgical treatment in a highly specialized multidisciplinary breast cancer clinic. The clinic serves a population of 237.000. The diagnostic tools routinely used are conventional mammography, ultrasound with core needle biopsy, and clinical examination including palpation of breast and axillary nodes. If indicated, the examination includes ultrasound examination and fine needle biopsy of axillary glands. We offer all patients selected for breast-conserving surgery preoperative breast MRI.

We include consecutively breast cancer lesions in women aged 35-75 in a prospective study, collecting data from January 2009 to December 2010. The patients are all selected for breast-conserving surgery based on the criteria recommended by the Norwegian Breast Cancer Group. That is, tumor ≤ 4 cm, or acceptable tumor:breast ratio, and age > 35. Multifocal lesions, defined as more than one tumor > 1 cm apart, size of tumor > 4 cm, or a large tumor:breast ratio, extensive ductal carcinoma in situ (DCIS), or known genetic disposition for breast cancer, indicates mastectomy according to these criterias. In addition, when postoperative radiation therapy is contraindicated, mastectomy is indicated. If the patients fill the criteria for breast-conserving surgery, they are offered preoperative breast MRI and included in the study. Patients who either choose mastectomy, or does not get a breast MRI for technical reasons, are excluded from the study. Two experienced breast radiologists evaluate the breast MRIs, and three experienced breast radiologists study the mammographies and perform the ultrasound examinations and biopsies. All additional MRI findings are examined by ultrasound-guided biopsy and given a histological diagnose before it influence the surgical method.

A formal application has been presented to the regional ethical commitee. Since this is an observational study of established practice, the commitee replied that approval was not required.

Inclusion Criteria:

• Patients ≥ 35 years and ≤ 75 years
• Indication for breast-conserving surgery according to criteria recommended by the Norwegian Breast Cancer Group:
• Tumor < 4 cm and acceptable tumor:breast ratio
• Tumor not infiltrating skin or pectoral fascia
• No multifocality (that is 2 foci or more, > 1 cm apart)

Exclusion Criteria:

• Patient choose mastectomy
• Technical problems with the MR machine
• Pacemaker
• Anxiety/claustrophobia

Patients are selected from screening or they are referred to the Breast Diagnostic Clinic for clinical symptoms. The clinic serves a population of 237.000 in Nordland county, Norway. Patients selected for breast-conserving surgery based on conventional radiological examination, that is bilateral mammography and ultrasonography with biopsy, are consecutively included in the study and offered preoperative breast MRI.