Abstract P4-02-12: Tomosynthesis as an alternative to magnetic resonance imaging (MRI) in assessing invasive lobular carcinoma (ILC) multifocality
Authors: Holt RE , Topps A , Lim YY , Gandhi A 
Published: March 2017

Abstract
Introduction
Invasive lobular carcinoma is associated with a higher rate of multifocality than other types of breast cancer. Breast MRI is commonly performed in patients diagnosed with ILC to assess for additional disease prior to formulating a management plan. MRI may be both time consuming and costly and can delay treatment.
Recently tomosynthesis has become an adjunct in the assessment and diagnosis of breast cancer. It is readily available at the time of mammography therefore providing information at the one stop clinic. We proposed that it may be possible to use tomosynthesis to assess for multifocality in ILC in place of MRI.
Method
A retrospective review of all cases of ILC diagnosed at a single regional screening unit over a 3-year period was performed. Patients having surgery as primary treatment were included. Ninety-eight patients were identified, 29 having both MRI and tomosynthesis in addition to mammography and ultrasound scan as part of their assessment. Histological data was used to compare the two imaging modalities. Bland and Altman limits of agreement analysis was performed to assess the difference between MRI and tomosynthsis in these patients. An acceptable difference (the difference in values that is unlikely to influence management) was set at 5mm.
Results
The Bland and Altman limits of agreement analysis produced three graphs to demonstrate the difference between MRI and Tomosynthesis, MRI and histology size and Tomosynthesis and histology size. It shows that the average difference between MRI and Tomosynthesis = 3.8mm (95% limits of agreement: –19.2 to 26.8mm). The percentage of 'acceptable' differences (defined as ≤ 5mm) was 72% for MRI and tomosynthesis suggesting that there is good concordance between the two. Tumours measuring &gt;30mm on MRI are perceived as smaller under Tomosynthesis.
The analysis demonstrated the average difference between MRI and histology values is -1.3 mm (95% limits of agreement = – 33.2 to 30.6)compared with an average difference between Tomosynthesis and histology of -5.1 mm (95% limits of agreement = – 27.7 to 17.5). The percentage of 'acceptable' differences (defined as ≤ 5 mm) was 48% for both MRI vs histology and Tomosynthesis vs histology, suggesting that neither is superior when compared to final histology results.
In three patients there were multifocal cancers identified on histology that had not been detected by any imaging modality. In one patient there were MRI images that suggested a second tumour which was not present on histological examination. The same is true for a patient diagnosed with a second cancer identified by tomosynthesis but not found in the specimen. A third patient was diagnosed with a second tumour by both image modalities but again not present on histology. In one case tomosysnthesis detected a true second cancer that was not identified on MRI.
Conclusion
We believe this preliminary study suggests that tomosynthesis is equivocal to MRI for assessing multifocality in ILC. If confirmed the implications would be a shorter investigative pathway with reduced delays and costs. A larger mutli-centre trial to assess the use of tomosynthesis to replace MRI in patients with ILC is warranted.
Citation Format: Holt RE, Topps A, Lim YY, Gandhi A. Tomosynthesis as an alternative to magnetic resonance imaging (MRI) in assessing invasive lobular carcinoma (ILC) multifocality [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-02-12.