Objective:To examine the imaging characteristics of mucinous breast carcinoma (MBC) in multi-parametric ultrasonography (mpUS), including conventional ultrasound, shear wave elastography (SWE), and contrast-enhanced ultrasound (CEUS), and evaluate their diagnostic efficacy for MBC.MethodsPatients admitted to Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine for consultation regarding breast lesions between January 2017 and April 2023 were retrospectively included in the study, with post-surgical resection pathology serving as the gold standard for diagnosis. Patients with fibroadenomas (FA) were randomly selected as controls from the same period of time in a 1∶1.5 ratio according to the random number table method. The imaging features were analyzed and classified according to the Breast Imaging Reporting and Data System (BI-RADS). Logistic regression was employed to identify valid diagnostic indicators, construct a prediction model, and generate the receiver operating characteristic curves for the subjects, allowing for the calculation of the area under curve (AUC). The AUC was used to assess the diagnostic efficacy.ResultsThe final sample included 40 lesions from 40 patients with MBC, comprising 16 cases of pure MBC (PMBC), 24 cases of mixed MBC (MMBC), and 60 FA lesions from 60 patients with FA. On conventional ultrasound, 50.0% (8/16) of PMBC were classified as BI-RADS category 3 and 4A, and 70.8% (17/24) of MMBC were classified as BI-RADS≥4B. In SWE, PMBC and MMBC were more frequently characterized by inhomogeneous hardness than FA (62.0% and 83.3% vs 25.0%), and a score of 3-4 was an independent predictor for distinguishing both from FA. In CEUS, the presence of cystic non-enhancing areas within the lesion and increased trophoblastic vessels at the margins were identified as independent risk factors for differentiating PMBC from FA. Compared with MMPC, mpUS demonstrated a significant improvement in the differential diagnosis of PMBC from FA when used in conjunction with conventional ultrasound (AUC: 0.949 vs 0.858, P<0.05).ConclusionMBC, particularly PMBC, is frequently underestimated due to its resemblance to fibroadenomas on conventional sonograms. The differential diagnosis of MBC and FA can be significantly enhanced by mpUS in comparison to conventional ultrasound alone.