Where reported, 35.1% of MRI-detected cancers were DCIS (mean size = 6.9 mm) and 64.9% were invasive cancers (mean size = 9.3 mm) [58]. MRI can accurately assess tumor size for preoperative planning [50,59-61]. In a study involving 343 tumors, size measurements of cancers on breast MRI were within 5 mm of pathological size in 88% of patients [60]. Still, other studies using mastectomy specimens have shown that MRI underestimates primary tumor size in 21% and overestimates primary tumor size in 24% of cases. MRI also overestimated the number of invasive lesions by 19% and underestimated the number of invasive lesions in 28% in the same study [62]. These data underscore the importance of using biopsy to pathologically confirm MRI findings before using them to alter surgical planning, especially when the MRI finding is nonmass enhancement [63]. In addition to tumor size assessment, some studies show a reduction in re-excision after preoperative MRI [64-68]. For example, in a study of 991 women, preoperative MRI changed the surgical procedure in 25% (157/626) of cases. In 81% (127/157), MRI was beneficial for the patients, as otherwise occult carcinomas were removed (n = 122) or further biopsy could be prevented (n = 5) [67]. In this trial, the rate of mastectomy did not differ between patients undergoing preoperative MRI and those who did not. A recent multinational observational study at 27 centers also found that subjects receiving MR as part of routine clinical care had a significantly lower reoperation rate after breast conservation (8.5% versus 11.7%, P < . 001) [69]. However, other large multicenter studies, such as the COMICE trial, showed the addition of MRI to conventional imaging was not significantly associated with a reduced reoperation rate, with 153 (19%) needing reoperation in the MRI group versus 156 (19%) in the non-MRI group, (OR, 0.96; 95% CI, 0.75-1.24; P = . 77) [70].
Imaging of Invasive Breast Cancer. Where reported, 35.1% of MRI-detected cancers were DCIS (mean size = 6.9 mm) and 64.9% were invasive cancers (mean size = 9.3 mm) [58]. MRI can accurately assess tumor size for preoperative planning [50,59-61]. In a study involving 343 tumors, size measurements of cancers on breast MRI were within 5 mm of pathological size in 88% of patients [60]. Still, other studies using mastectomy specimens have shown that MRI underestimates primary tumor size in 21% and overestimates primary tumor size in 24% of cases. MRI also overestimated the number of invasive lesions by 19% and underestimated the number of invasive lesions in 28% in the same study [62]. These data underscore the importance of using biopsy to pathologically confirm MRI findings before using them to alter surgical planning, especially when the MRI finding is nonmass enhancement [63]. In addition to tumor size assessment, some studies show a reduction in re-excision after preoperative MRI [64-68]. For example, in a study of 991 women, preoperative MRI changed the surgical procedure in 25% (157/626) of cases. In 81% (127/157), MRI was beneficial for the patients, as otherwise occult carcinomas were removed (n = 122) or further biopsy could be prevented (n = 5) [67]. In this trial, the rate of mastectomy did not differ between patients undergoing preoperative MRI and those who did not. A recent multinational observational study at 27 centers also found that subjects receiving MR as part of routine clinical care had a significantly lower reoperation rate after breast conservation (8.5% versus 11.7%, P < . 001) [69]. However, other large multicenter studies, such as the COMICE trial, showed the addition of MRI to conventional imaging was not significantly associated with a reduced reoperation rate, with 153 (19%) needing reoperation in the MRI group versus 156 (19%) in the non-MRI group, (OR, 0.96; 95% CI, 0.75-1.24; P = . 77) [70].