［Introduction］ In recent years, ultrasound（US）has revealed various characteristics of breast cancer. We have reported on the imaging characteristics of triple-negative breast cancer, but the majority of subtypes are luminal, and only morphological characteristics have been identified. Therefore, we hypothesized that morphological characteristics may be closely related to the tumor's proliferation potential. We focused on Ki67 values, which are related to the rate of cell division in tumor growth, and examined the relationship between Ki67 values, an indicator of proliferation potential, and morphological characteristics on US.
　［Subjects and Methods］ Of 166 cases of invasive cancer that were histologically confirmed at our hospital from June 2023 through May 2024, we compared the US images of 154 cases that were determined to be tumors by US with Ki67 values to examine their characteristics. Furthermore, the cutoff for Ki67, with a low value of less than 5％ and a high value of 30％ or more, is highly reproducible and suitable for clinical practice. As our aim was to evaluate the morphological characteristics of low and high values, intermediate values were excluded from the study, and in this study, a low value of 10％ or less（33 cases）and a high value of 30％ or more（66 cases）were used.
　［Conclusion］ In this study, the items that showed significant differences were the shape, margin, depth and ratio. Therefore, it was suggested that morphological differences were observed due to differences in proliferative capacity. In other words, tumors with high proliferative capacity showed expansive growth, while those with low proliferative capacity showed the invasive form. In breast cancers exhibiting these characteristics, it was suggested that it may be possible to infer the proliferative capacity of the tumor from imaging findings, rather than simply identifying it as breast cancer.

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　In recent years, vacuum-assisted large core needle biopsy (VAB) has become a widely used technique for lesions suspected of breast malignancy. While the diagnostic accuracy of biopsies improves as the specimen volume increases, there are cases in which all of the lesion is removed during VAB. In this report, we describe a case of breast cancer diagnosed by VAB without malignant findings in the surgical specimen.
　We retrospectively validated cases with no malignant findings in surgical specimens from January 2014 to December 2020 although breast cancer was diagnosed by VAB performed at our hospital. Patients who underwent preoperative drug therapy were excluded.
　Eleven patients were included in the study during the relevant period. The median age at diagnosis was 53 years. Nine patients had ductal carcinoma in situ and 2 had invasive ductal carcinoma. The most common ultrasonographic finding was a localized lesion (8 cases) with a median length of 7 mm.
　When performing VAB on small localized lesions, placement of ultrasound-visible markers and detailed documentation of lesion location seem necessary.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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