Patient selection
Consecutive data of patients with MRI-detected enhancing lesions who have undergone MRI-guided percutaneous biopsy in 2018 from three tertiary hospitals: Sinai Health System, University Health Network, and Women's College Hospital, affiliated with the University of Toronto were retrospectively reviewed. The patient's informed consent was waived. Only those who have undergone surgical excision or were followed clinically or by imaging for at least one year from the date of the last imaging examination were included.
All patients had ultrasound or mammography before MRI, but the included lesions did not have mammography or ultrasound correlated lesions. The included lesions had BIRADS 4 or 5 in enhanced MRI, which make them candidate for MRI guided biopsy. Patient's demographics and MRI findings, imaging-guided biopsy results, and if applicable, the pathological outcome after excisional surgery were reviewed.
Imaging technique
MRI was performed using state-of-the-art equipment and standard-of-care technique following American College of Radiology (ACR) quality standards [25]. In all cases, MRI examinations were performed on a 1.5-T system (Signa Excite, GE Medical Systems) or Espree or Avanto (Siemens Healthcare) and 3.0-T system (Verio; Siemens Healthcare) with a standard, bilateral, dedicated breast coil (Sentinelle Vanguard; Sentinelle Medical, Inc.). The sequences included precontrast axial T1, T2-weighted images with fat suppression, and dynamic contrast-enhanced (DCE) T1-weighted imaging sequences. The DCE sequence consisted of a pre-contrast scan and four post-contrast scans. MRI examinations for premenopausal patients were scheduled in the second week of the menstrual cycle to minimize enhancement of benign breast parenchyma (25).
Imaging interpretation
All MRI data were reviewed by two breast fellowship-trained radiologists (AA,12 years of experience, VF, 20 years of experience) from the same department that were blinded to the surgical or core needle biopsy pathology results and the clinical outcomes. The readers described MRI findings following the Breast Imaging Reporting and Data System (BIRADS) lexicon [25, 26]. Discrepant results of lesion characteristics between radiologists were assessed by consensus. The imaging studies with final assessment category BI-RADS 4 and BI-RADS 5 were considered positive, and all other results were considered negative.
Demographic data were recorded, including age, personal history of breast cancer, risk factors including genetic mutation, and family history of breast cancer. In addition, the MRI indication (screening; staging; surveillance; problem-solving; others) and imaging findings were retrieved (parenchymal enhancement; T1 signal, T2 signal, mass or non-mass enhancement; shape and margin for masses; and enhancement pattern and distribution for non-mass enhancement, and dynamic pattern).
Interventional procedures and pathology
Percutaneous MRI-guided biopsies were performed by attending breast imaging experienced radiologists at the same hospital within 3 weeks from the enhanced MR, using a 9-gauge MRI-compatible vacuum-assisted device (ATEC, Suros Surgical systems), with 8 to 12 samples obtained.
Histopathology
The histopathologic result from the MRI-guided biopsy was considered the reference standard for lesion evaluation. Invasive cancer and ductal carcinoma in situ (DCIS) were considered malignant histopathological results. The histological results, including papillary lesions, complex sclerosing lesions (CCL), radial scar (RS), atypical ductal hyperplasia (ADH), atypical lobular hyperplasia (ALH), and lobular carcinoma in situ (LCIS) were categorized as high-risk lesions (HRL). Other pathologies are considered benign (fibrocystic changes, Pseudoangiomatous stromal hyperplasia, columnar cell changes or hyperplasia, focal fibroadenomatoid changes, stromal fibrosis). Patients with malignancy had surgical excision as per standard institutional practice. In addition, surgery was performed in some of biopsy-proven high-risk lesions, and benign pathology after multidisciplinary discussion, and based on patient’s and surgeon preferences.
All included women who did not undergo excisional surgery had a minimum of 12-month follow-up. The standard follow-up was a clinical exam, mammogram alone, or mammogram supplemented by MRI.
Statistical methods
Summary statistics such as means, medians, standard deviations, ranges, frequencies and proportions were reported to describe participant demographical and clinical characteristics. Wilcoxon rank sum test or Chi-square test was used to compare participant characteristics across pathology groups. Logistic regression model was used to evaluate the correlation between participant characteristics with true positive result for the main data set and subgroup analysis. Subgroup analysis was conducted for participants with mass and non-mass lesions, respectively.