Abstract: Background and purpose: The large-scale use of full-field digital mammography (FFDM) can significantly reduce the mortality rate of breast cancer. However, the sensitivity and specificity of diagnosis were significantly reduced in patients with dense breast. This study aimed to compare the efficacy of digital breast tomosynthesis (DBT) with conventional imaging methods in assessing the tumor size before surgery. Methods: One hundred and thirty-six patients diagonosed as having breast cancer by pathology were enrolled in this study. All patients underwent FFDM, DBT and breast magnetic resonance imagining (MRI) examinations between Mar. 2015 and Dec. 2015. The maximum tumour size was measured by 3 experienced radiologists and compared to the gross specimen using Pearson analysis. The results were compared between any two methods using paired t test. Results: One hundred and forty masses were found in 136 patients, and 26 masses were excluded from the patients who received operation after adjuvant chemotherapy. One hundred and fourteen masses with measurable tumour size were included for further research. There was no significant difference in the maximum tumour size between DBT or MRI group and gross specimen group (both P>0.05), while there was remarkable difference between the gross specimen group and FFDM (t=3.30, P=0.013 4), or the sonography (t=2.58, P=0.021 5) group. The coefficients of correlation with pathological data of DBT (r=0.81) and MRI (r=0.84) were significantly higher than those of sonography (r=0.68) and FFDM (r=0.69). Conclusion: DBT and MRI are superior to FFDM and sonography in the preoperative assessment of breast tumor size. As a new mammography technology, DBT has good clinical application prospect in preoperative staging of breast cancer.

Key words: Breast tumor, Full-field digital mammography, Magnetic resonance imaging, Digital breast tomosynthesis, Sonography