Objective The aim of this study is to evaluate the diagnostic value of shear wave elastography (SWE) added to conventional ultrasound (US) in the diagnosis of small (2 cm) breast cancer.Methods Among patients who underwent SWE and US before biopsy or surgical operation , 171 patients with 177 small (≦2 cm) breast lesions were enrolled in this study.Diagnostic performances of each quantitative SWE parameters were calculated by receiver operating characteristic (ROC) curves. Performances of conventional US and US combined to SWE was also compared.And the diagnostic value of Emax in small Breast Imaging Reporting and Data System (BI-RADS) category 4a lesions.Histologic diagnosis was used as a reference standard.Results Of the 177 lesions, 22 lesions (12.4%) were malignant and 155(87.6%) were benign.SAll average quantitative elastography values were signi?cantly higher in malignant comparing with benign lesions(P<0.05).Az value of combined Emax with US was signi?cantly lower than that of conventional US alone (P<0.05).SBy using cutoff of Emax 87.5Kpa for downgrading BI-RADS category 4a lesions to category 3, 76/94 category 4a lesions (80.9%) were downgraded.SAfter downgrading, 5 cancers were missed and the malignancy rate of category 3 lesions increased from 0% (0/55) to 3.8% (5/133) (P <0.05).