为了评估乳腺癌诊断妇女的乳腺X线密度与偶然发现的磁共振成像（MRI）病灶数量和病灶恶性可能性之间的相关性。根据EUSOBI和EUSOMA术前乳腺MRI的标准，在我们的机构，诊断为乳腺癌的患者通常在MRI之前进行乳腺X线检查和超声检查。在MRI中检测到的可疑乳腺病灶会进行活检。我们纳入了2014年至2019年期间诊断为浸润性乳腺癌并进行术前乳腺MRI检查的患者。根据BI-RADS词汇表第5版，一位读者对乳腺密度进行了回顾性分类。 在973例恶性原发性乳腺肿瘤中，共有946例患者中的166例（17.5%）出现了共计175例（18.0%）的偶然MRI检测到的病灶（82例（46.9%）恶性和93例（53.1%）良性）。根据BI-RADS，高乳腺密度与术前乳腺MRI中所有偶然增强病灶的发生率相关：较A类相比，对于B类的发生率较高，为2.66（95%置信区间：1.03-6.86），对于C类为2.68（1.04-6.92），对于D类为3.67（1.36-9.93）（p < 0.05）。然而，高乳腺密度并不预示着恶性偶然发现病灶的发生率更高（p = 0.741）。在对侧乳房中发现的偶然MRI检测到的病灶很可能是良性的（p < 0.001）：对侧乳房中有18例（27.3%）/48例（72.7%）恶性/良性偶然病灶，而同侧乳房中有64例（58.7%）/45例（41.3%）恶性/良性偶然病灶。 诊断为乳腺癌且乳房密度高的妇女存在更多偶然发现的MRI病灶，但乳房密度高并不意味着恶性偶然病灶的可能性增加。在乳腺癌诊断的妇女中，密度高的乳房不应被视为术前乳腺MRI的指征。 • 对于乳房密度高并诊断为乳腺癌的患者，术前MRI的作用仍有争议。 • 乳房密度较高的妇女的术前MRI检测到的所有偶然乳腺病灶的发生率较高，但与脂肪乳房的妇女相比，恶性偶然发现的MRI病灶的发生率并不高。 • 仅仅因为乳房密度高并不应作为进行术前乳腺MRI的指征。 © 2023. 作者。

To assess whether mammographic breast density in women diagnosed with breast cancer correlates with the total number of incidental magnetic resonance imaging (MRI)-detected lesions and the likelihood of the lesions being malignant.Patients diagnosed with breast cancer meeting the EUSOBI and EUSOMA criteria for preoperative breast MRI routinely undergo mammography and ultrasound before MRI at our institution. Incidental suspicious breast lesions detected in MRI are biopsied. We included patients diagnosed with invasive breast cancers between 2014 and 2019 who underwent preoperative breast MRI. One reader retrospectively determined breast density categories according to the 5th edition of the BI-RADS lexicon.Of 946 patients with 973 malignant primary breast tumors, 166 (17.5%) had a total of 175 (18.0%) incidental MRI-detected lesions (82 (46.9%) malignant and 93 (53.1%) benign). High breast density according to BI-RADS was associated with higher incidence of all incidental enhancing lesions in preoperative breast MRIs: 2.66 (95% confidence interval: 1.03-6.86) higher for BI-RADS density category B, 2.68 (1.04-6.92) for category C, and 3.67 (1.36-9.93) for category D compared to category A (p < 0.05). However, high breast density did not predict higher incidence of malignant incidental lesions (p = 0.741). Incidental MRI-detected lesions in the contralateral breast were more likely benign (p < 0.001): 18 (27.3%)/48 (72.7%) vs. 64 (58.7%)/45 (41.3%) malignant/benign incidental lesions in contralateral vs. ipsilateral breasts.Women diagnosed with breast cancer who have dense breasts have more incidental MRI-detected lesions, but higher breast density does not translate to increased likelihood of malignant incidental lesions.Dense breasts should not be considered as an indication for preoperative breast MRI in women diagnosed with breast cancer.• The role of preoperative MRI of patients with dense breasts diagnosed with breast cancer is under debate. • Women with denser breasts have a higher incidence of all MRI-detected incidental breast lesions, but the incidence of malignant MRI-detected incidental lesions is not higher than in women with fatty breasts. • High breast density alone should not indicate preoperative breast MRI.© 2023. The Author(s).