Objective: Patients preoperatively diagnosed with ductal carcinomain situ (DCIS) by core needle biopsy (CNB) exhibit a significant risk for upstaging on final pathology, which leads to major concs of whether axillary staging is required at the primary operation. The present study aimed to identify clinicopathological factors associated with upstaging in patients preoperatively diagnosed with DCIS by CNB. Methods: The present study enrolled 604 patients (cN0M0) with a preoperative diagnosis of pure DCIS by CNB, who underwent axillary staging between August 2006 and December 2015, at Fudan University Shanghai Cancer Center (Shanghai, China). Predictive factors of upstaging were analyzed retrospectively. Results: Of the 604 patients, 20.03％ (n = 121) and 31.95％ (n = 193) were upstaged to DCIS with microinvasion (DCISM) and invasive breast cancer (IBC) on final pathology, respectively. Larger tumor size on ultrasonography (> 2 cm) was independently associated with upstaging [odds ratio (OR) 1.558,P = 0.014]. Additionally, patients in lower breast imaging reporting and data system (BI-RADS) categories were less likely to be upstaged (4Bvs. 5: OR 0.435,P = 0.002; 4Cvs. 5: OR 0.502,P = 0.001). Overall, axillary metastasis occurred in 6.79％ (n = 41) of patients. Among patients with axillary metastasis, 1.38％ (4/290), 3.31％ (4/121) and 17.10％ (33/193) were in the DCIS, DCISM, and IBC groups, respectively. Conclusions: For patients initially diagnosed with DCIS by CNB, larger tumor size on ultrasonography (> 2 cm) and higher BI-RADS category were independent predictive factors of upstaging on final pathology. Thus, axillary staging in patients with smaller tumor sizes and lower BI-RADS category may be omitted, with little downstream risk for upstaging.