Objective: We evaluated ultrasonographic findings and the corresponding histopathological characteristics of breast cancer patients with Breast Imaging Reporting and Data System (BI-RADS) category 1 mammogram. Methods: We retrospectively reviewed the ultrasonographic findings and the corresponding histopathological features of 45 breast cancer patients with BI-RADS category 1 mammogram and 537 controls with mammographic abnormalities. We evaluated the ultrasonographic findings including mass shape, periphery, internal and posterior echo pattern, interruption of mammary borders and the distribution of low-echoic lesions, and the corresponding histopathological characteristics including histological classification, hormone receptor and human epidermal growth factor receptor 2 status of invasive ductal carcinoma and ductal carcinoma in situ, histological grade, mitotic counts and lymphovascular invasion in individual cases of BI-RADS category 1 mammograms and compared with those of the control group. Results: The ultrasonographic characteristics of the BI-RADS category 1 group were characterized by a higher ratio of round shape (P< 0.001), non-spiculated periphery (P = 0.021), non-interruption of mammary borders (P< 0.001) and non-attenuation (P = 0.011) compared with the control group. A total of 52.6% of low-echoic lesions were associated with spotted distribution in the BI-RADS 1 group, whereas 25.8% of low-echoic lesions were associated with spotted distribution in the control group (P = 0.012). As for histopathological characteristics, there was a statistically higher ratio of triple-negative subtype (P = 0.021), and this particular tendency was detected in histological grade 3 in the BI-RADS category 1 group (P = 0.094). Conclusion: We evaluated ultrasonographic findings and the corresponding histopathological characteristics for BI-RADS category 1 mammograms and noted significant differences among these findings in this study. Evaluation of these ultrasonographic and histopathological characteristics may provide a more accurate ultrasonographic screening system for breast cancer in Japanese women.
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