Bernard, J

627 Background: With more centers using MRI to aid in initial staging, there is apprehension that the highly sensitive MRI exam may lead to “unnecessary” mastectomies. We evaluated whether a negative contralateral MRI could be used to rule out a synchronous contralateral carcinoma and hence avoid a prophylactic contralateral mastectomy (CPM) at initial breast cancer diagnosis. Methods: Data of women with a new diagnosis of breast cancer (invasive or DCIS) from February 2003-November 2007 at our institution were reviewed. Women who had a negative MRI of the contralateral breast and who subsequently underwent CPM were included. A CPM was one in which there was no histological confirmation of cancer in the contralateral breast before surgery. All mastectomy specimens were analyzed pathologically. True negatives were mastectomy samples which contained no cancer following pathologic examination. False negatives were mastectomy samples which were found to have cancer after pathologic review. Results: 538 women were identified. 51 women met the study criteria. Median patient age was 56 years (range, 33–77). Of the 51 women who underwent a CPM, 2 were found to have pathologic confirmation of cancer. One occult cancer was a 0.3 cm grade 1, invasive lobular carcinoma; the second a 0.5 cm, low grade DCIS. The overall prevalence of synchronous occult contralateral cancer after a negative MRI was 3.9% (95% CI 0.5 - 13.5%). The negative predictive value of MRI was 96.1% (95% CI 86.5 - 99.5%). Conclusions: This study provides pathologic data regarding the utility of a negative contralateral breast MRI in women with newly diagnosed breast cancer. The prevalence of a synchronous occult contralateral cancer after a negative MRI in women with newly diagnosed breast cancer is very low. Physicians and patients can be assured that the risk of occult cancer is low in the setting of a normal contralateral MRI, an important fact when considering CPM after a diagnosis of unilateral breast cancer. No significant financial relationships to disclose.

614 Background: An analysis of preoperative bilateral breast MRI at our institution suggests that approximately 1/3 of patients with newly diagnosed breast cancer may have a mammographically occult, but MRI-evident, contralateral breast abnormality. A number of these patients will have pathologic confirmation of carcinoma in the contralateral breast. Identification of risk factors to predict which patients are at high risk for having a mammographically occult contralateral carcinoma was performed. Methods: MRI results of 401 women with newly diagnosed breast carcinoma who underwent MRI were reviewed (overall group; OG). Patients with a contralateral abnormality identified only by MRI were analyzed to determine the incidence of contralateral carcinoma. In addition, the following risk factors were evaluated: Age at diagnosis, menopausal status, tumor size, nodal status, ipsilateral tumor histology, tumor grade, hormone receptor status, Her-2/neu receptor status, and whether the patient had a palpable vs. mammographically detected abnormality. Results: Pathologically confirmed contralateral carcinoma (CC) was found in 13 patients (3.2%). Similar percentages of patients in both groups (OG and CC) were noted in regard to tumor size, histology, grade, nodal status, Her-2/neu receptor status, and method of detection (palpable vs. mammographic). However, median patient age was 71 (CC) vs. 62(OG); 92% (12/13) were postmenopausal (CC) compared to 75% (OG); and 100% were ER positive (CC) vs. 81% percent (OG). Conclusions: Older, postmenopausal women who have ER + tumors may have a higher likelihood of having synchronous, contralateral, mammographically occult, MRI-detected breast carcinoma. Preoperative MRI may be beneficial in patients with similar risk factors; however, further follow up and additional experience is needed for confirmation of these findings. No significant financial relationships to disclose.