Ultrasound features and clinicopathologic correlations of breast adenoid cystic carcinoma: a retrospective observational study.

BACKGROUND: Adenoid cystic carcinoma of the breast (ACCB) is a rare form of triple-negative breast cancer characterized by generally indolent but variable clinical behavior. Despite distinct pathological and molecular features, its ultrasound characteristics remain poorly defined. This study aimed to describe the sonographic and clinicopathologic features of ACCB. METHODS: This retrospective study reviewed histologically confirmed cases of ACCB diagnosed at a tertiary medical center between June 2015 and June 2025. Demographic, clinical, ultrasound, and pathological data, including MYB status, were collected. Differences in sex distribution and age at diagnosis between patients with ACCB and the overall breast cancer cohort during the same period were compared. Sonographic parameters included lesion size, shape, margin, internal echogenicity, posterior acoustic features, presence of calcifications, and vascularity. Descriptive statistics were used to summarize clinical and imaging features, and group comparisons were performed using the Mann-Whitney U and Fisher's exact tests, as appropriate. In addition, exploratory deep image feature analysis was performed using representative ultrasound images. RESULTS: Twelve patients (11 women, 1 man; median age 60.5 years) were identified. Most lesions showed malignant ultrasound features, most commonly irregular shape (11/12) and hypoechogenicity (12/12); indistinct margins were observed in seven cases. Calcifications were present in ten lesions, and posterior acoustic shadowing in two. All lesions were categorized as Breast Imaging Reporting and Data System (BI-RADS) categories 4-5. Histologic subtypes included classic [6], solid-basaloid [5], and mixed [1]; MYB rearrangement was detected in all cases. Axillary lymph node metastases were observed in two patients, both with the solid-basaloid subtype. During follow-up, three patients (25%) developed distant metastases. Exploratory deep image feature analysis did not reveal distinct clustering patterns among histologic subtypes. CONCLUSIONS: ACCB generally exhibits malignant ultrasound features and is typically categorized as BI-RADS 4-5, but lacks disease-specific imaging characteristics. Histopathologic and molecular confirmation, particularly MYB rearrangement testing, remains essential for accurate diagnosis. The occurrence of nodal and distant metastases in a subset of patients indicates that careful clinical follow-up remains necessary.