Comparative effectiveness of positron emission mammography and MRI in the contralateral breast of women with newly diagnosed breast cancer.

OBJECTIVE The objective of our study was to compare the performance of positron emission mammography (PEM) with that of MRI in the evaluation of the contralateral breast of women with newly diagnosed cancer. SUBJECTS AND METHODS Four hundred seventy-two women with newly diagnosed breast cancer offered breast-conserving surgery from September 2006 through November 2008 consented to participate in a multicenter protocol. Participants underwent contrast-enhanced breast MRI and 18F-FDG PEM in randomized order, and the examinations were interpreted independently. The performance characteristics of the imaging modalities were compared using the McNemar test and generalized estimating equations. A retrospective blinded review of PEM images was performed by four experienced observers to understand the reasons for false-negatives. RESULTS Three hundred sixty-seven women (median age, 58 years; age range, 26-93 years) eligible for analysis completed the appropriate follow-up for study inclusion. Fifteen women (4.1%) were found to have contralateral cancer (11 invasive [mean tumor size, 12 mm; median, 10 mm; range, 1-22 mm] and four ductal carcinoma in situ). Of the 15 cases, both PEM and MRI showed three (20%), only MRI showed 11 (73%), and one (6.7%) was found at prophylactic mastectomy. MRI sensitivity at 14 of 15 (93%; 95% CI, 66-94) was higher than PEM at three of 15 (20%; 95% CI, 5.3-46) (p<0.001). On PEM, three additional cancers were seen prospectively but were considered probably benign and two other cancers were visible in retrospect at the site. Of 352 contralateral breasts without cancer, findings were negative or benign on PEM for 335 (95.2%; 95% CI, 92.2-97.0), which is more than MRI at 315 (89.5%; 95% CI, 85.7-92.4; p=0.002). The positive predictive value (PPV) of PEM-prompted biopsies (3/14 [21%]) was not significantly different from the PPV of MRI (15/54 [28%], p=0.58). On blinded retrospective PEM review of the 15 contralateral cancers, PEM findings for 11 (73%) were considered suspicious. CONCLUSION Contralateral cancer was found in 15 of 367 women (4.1%), with MRI showing 14 (93%). Eleven contralateral cancers (73%) were visible on PEM, but only three (20%) were recognized prospectively as suspicious. Lesions that are visible on PEM should be viewed as suspicious unless known to be benign by prior breast imaging or biopsy.