Ultrasonographic and clinicopathological findings of breast cancers measuring 5 mm or less detected on ultrasonography

Abstract

Purpose: In recent years, small breast cancers have been increasingly detected using ultrasonography (US). According to the recall criteria established by the Japan Association of Breast and Thyroid Sonology (JABTS), a mass measuring ≤5 mm and lacking ultrasonographic findings of invasion does not require further examination, and only masses with irregular margins should undergo further examinations. However, the small size of these lesions makes it difficult to evaluate their morphology. Therefore, to contribute to future US judgement, this study aimed to examine how breast cancers identified as solid masses measuring ≤5 mm on US were detected and what type of breast cancer they constituted. Subjects and Methods: We retrospectively reviewed the histopathologic types, subtypes, patient backgrounds, detection opportunities, and US findings of breast cancer lesions measuring ≤5 mm with confirmation on US among consecutive cases operated on at our hospital from May 2016 to April 2021. Results and Discussion: Sixteen patients with 16 lesions were included: eight with invasive carcinoma and eight with ductal carcinoma in situ (DCIS). All patients were unaware of their status, and lesions were detected on screening or surveillance, or as incidental lesions during preoperative examinations for other breast cancers. Excluding patients with hereditary breast ovarian cancer syndrome, all patients had hormone receptor-positive low-grade breast cancer, indicating that these cancers might not have affected the patients’ prognosis whether they were detected at that time or at the next year’s screening. Conclusion: Invasive US findings can accurately determine invasive cancer, even for masses measuring ≤5 mm. In the JABTS diagnostic tree, masses measuring ≤5 mm without invasive findings are basically considered to not require a further examination. All of the average-risk cases were low-grade DCIS even in the present results. It is necessary to consider overdiagnosis and overtreatment in the future.