Bi-rads category 3 breast lesions on MRİ; follow-up results

Our aim is to determine the frequency of BI-RADS category 3 lesions detected on MRG and analyze the malignancy rate in these lesions diagnosed under our criteria. Also to present MRI findings and to evaluate the patient compliance to our short-term follow-up protocol are our secondary purposes. We conducted this study retrospectively and after the permission of our ethic committee (Number: 70904504/115, Board Code: 2012-KAEK-20 / Date: 12.03.2018). From our PACS and hospital information systems (MEDI-HASTA 16.43 1997-2014, MIA-MED 1.0.1.3181 2014-2016, Siemens Leonardo Workstation 2009, SECTRA PACS IDS7 18.2.14.4021 2016), we found 913 patients undergone dynamic breast MRI between June 2014 and February 2018. Of these, 187 women had BI-RADS category 3 assessment. We excluded the patients who are not completing or participating to our follow-up protocol and whose biopsy results are not available. Finally 69 patients with 132 category 3 lesions, whose follow-up results and/or annual reports are available, composed our study group. We evaluated MRI findings comparing by mammography and US findings in these patients. Our short-term follow-up protocol on MRI is composed of three examinations at 6-month intervals for first year, and final examination at 24thmonth. Besides, we recommend age –appropriate screenings for the patients whose lesion is stabile after two years. If the category 3 lesions on MRI is seen also on mammography and/or US, we recommend to go on follow-ups with these modalities instead of MRI. The detection frequency, the malignancy rate, negative predictive value, the compliance with our follow-up protocol considering 95% CI were analyzed. The detection frequency on MRI for BI-RADS category 3 lesions was 20.5%. The distribution of MRI findings was as follows: 77.3% mass, 11.4% nonmasslike contrast enhancement, 4.5% focus, 6.9% lymph node. In total, seven lesions underwent core or excisional biopsy, which we recommend biopsy four of them because of interval progression during follow-ups. Biopsy yielded invasive ductal carcinoma in only one lesion (T1N0M0) showing ductal contrast enhancement on MRI. Our NPV was 99,2% (95% CI: from 98,38% to 100,09%). The malignancy rate was calculated as 0.8% (95% CI: from 0.15% to 1.85%). Of 69 patients, 89% of them complied our follow-up protocol by attending at least twice. As a conclusion, malignancy rate with a 0.8% rate is very low in BI-RADS category 3 lesions detected on MRI similar to low malignancy rate provided with mammography and ultrasound. Our criteria meet sufficiently the definition of BI-RADS category 3 on MRI. Key words: Breast, MRI, BI-RADS category 3