Purpose

Invasive breast cancer most commonly presents as enhancing mass on magnetic resonance (MR) imaging, and it is occasionally accompanied by nonmass enhancement (NME) surrounding the index mass. However, there has been no data regarding the significance of accompanying NME. Therefore, the purpose of this study was to investigate the significance of accompanying NME in invasive ductal carcinoma (IDC) on preoperative MR imaging and assess the factors affecting the significance.

Methods

The institutional review board of our institution approved this retrospective analysis, and the need for informed consent was waived. Between January 2015 and February 2016, 163 consecutive patients (median age, 54 years; range, 32 to 79 years) with IDC who underwent preoperative MR and subsequent surgery were enrolled and reviewed. All MR examinations were performed using a 3.0-T MR imager (Achieva; Philips Medical System, Best, Netherlands) with a dedicated, sensitivity encoding (SENSE) –enabled, four-channel breast coil in the prone position. All images were acquired with bilateral axial views. MR imaging was retrospectively interpreted by two radiologists in consensus according to the BI-RADS® Atlas without information of histopathology. 1Maximum diameter measurements were assessed by using a combination of precontrast and early post-contrast fat-suppressed T1-weighted and subtraction images. First, only size of index cancer mass was measured in the largest dimension among transverse, sagittal and coronal planes. Second, total extent of mass and accompanying NME was measured. Accompanying NME was defined NME lesions around the index mass less than 1cm apart. Preoperative tumor size on MR imaging was compared to pathologic tumor size. Tumor size measurement on MR imaging within 5 mm of histopathological measurement were considered concordant. After comparing the size between by MR and pathology, accompanying NME results was assessed. Positive NME was defined as pathological result of malignancy. To identify affecting factors associated with frequency of accompanying NME and positive pathologic result, clinicopathologic features were compared using the Student t-test or Chi-square test.

Results

Of the 163 invasive breast cancers, 123(75.5 %) cancers presented as only mass feature and 40(24.5 %) cancers had accompanying NME around the index mass. The concordance rate within 5 mm between mass size by MR and IDC size by pathology was 91.9 % (113 of 123) in breast cancer without NME and 72.5 % (29 of 40) in cancer with accompanying NME, there was significant difference (P = .005). Breast cancers with rim enhancement pattern and HER2 positivity were more frequently had accompanying NME on MR images (P = .017 and .007, respectively). Of the 40 accompanying NME, 22 (55%) had positive pathologic results and 18 (45%) had negative results. Accompanying NME in HER2 positive breast cancer was more frequently had positive pathologic results than HER2 negative breast cancers (84.6% [11 of 13] vs. 40.7% [11 of 27], P= .016).

Discussion

NME were the known major cause of false-positive breast MR findings. A study reported that the false positive rate of NME was 48 %, it is significantly high rate compared with mass lesions.2 However, we found 55% accompanying NME on preoperative MR imaging had malignant pathologic results. This value is suitable for BI-RADS category 4 that shouldn’t be ignored finding in MR imaging. Drawbacks to the high false positive rate of NME on MR images, it is necessary to find the affecting factors associated with increase positive predictive values. In our study, IDC with rim enhancement on MR and positive HER2 status was frequently accompanied by NME in preoperative MR images. Moreover, positive HER2 status was significantly associated with positive pathologic result of NME. There was no previous study about the association with hormonal subtype and significance of NME. This study has limitation. This was a retrospective study from a single institution with a relatively small number of patients. The final result was investigated from the comparison between MR images and pathologic report without direct preoperative mapping. Therefore, in case of negative results, we did not know what kind of benign pathology was.

Conclusion

Our data demonstrated that accompanying NME with IDC on preoperative MR images had clinically significant result, yielding a 55% positive pathologic results. The HER 2 positive IDC was more frequently accompanied by NME and associated with positive pathologic results. Our result suggests that the accompanying NME should be carefully investigated on preoperative MR images and individually determined according to molecular subtypes. These observations may inform future clinical practice validated in prospective trials.

Acknowledgements

No acknowledgement found.

References

1. Morris EA, Comstock CE, Lee CH (2013) ACR BI-RADS® Magnetic Resonance Imaging. In: ACR BI-RADS® Atlas, Breast Imaging and Reporting and Data System, Reston, VA, American College of Radiology 2. Baltzer PA, Benndorf M, Dietzel M, Gajda M, Runnebaum IB, Kaiser WA. False-positive findings at contrast-enhanced breast MRI: a BI-RADS descriptor study. AJR Am J Roentgenol 2010;194(6):1658-1663.