BI-RADS® category 3 lesions on breast MR imaging in women at genetic risk of cancer: A 3-year retrospective analysis

Objectives. - The objectives of the study were to evaluate the frequency of MRI BI-RADS (R) category 3 mammary lesions, to describe the MRI descriptors and to calculate the cancer rate (2-year follow-up) of such lesions in a population at high-risk of breast cancer. Materials and methods. - Among 3222 MRI studies in high-risk population between January 2016 and December 2018, 94 patients were identified (mean age: 43.5 years, gene mutation: 78.7 %) with 112 category 3 lesions. Clinical data, initial MRI studies (two radiologists recorded initial descriptors from the MRI BI-RADS (R) lexicon and a category assessment was performed by the expert reviewer). Pathologic results and 2 years of follow-up imaging findings were analysed. Fisher and Chi2 tests compared the lesion descriptors between prevalent versus incidental rounds, categories 1-2 versus 3 from the expert assessment and benign lesions versus cancers (significant P < 0.05). Results. - The mean BI-RADS category 3 annual rate was 4.7 %. Lesions included 39 % of masses (91 % measured 10 mm or less, circumscribed margin: 100 %), non mass enhancement in 33 % (65 % were 10 mm or less, focal distribution: 65 %, homogeneous enhancement: 89 %) and focus in 28 % (there was no significant difference between prevalent versus incidental rounds). The expert review downstaged 43 % of lesions as benign (there was no significant difference with category 3 lesions). The follow-up compliance rate was 76.7 % at 6 months. The cancer rate was 5.4 %: five invasive pT1N0 cancers were diagnosed at initial post-MRI evaluation (n = 3) and at 6 months (n = 2), and one phyllodes sarcoma at one year (there was no intermediate MRI study). A washout kinetic curve was the only significant parameter for differentiating benign from malignant lesions (P= 0.008). Conclusion. - If the rate of category 3 MRI lesions is less than 10 % as recommended in popu-lations at high-risk of breast cancer, the cancer rate is over 2 %. Any lesion identified on post-MRI targeted imaging and/or exhibiting a washout dynamic curve should be sampled. When a surveillance is initiated, cancers may be detected at 6-months. (c) 2022 Elsevier Masson SAS. All rights reserved.