Abstract: Objective To explore the clinical and pathological characteristics of 110 interval cancer cases in first three rounds breast cancer screening of Shunyi District. Methods The breast cancer incidence registration system and the database of breast cancer screening were linked to identify the interval cancer cases. The characteristics of interval breast cancers were compared with breast cancers from the outpatients among the same period. Results Compared with breast cancer outpatients， interval cancer cases were younger and of smaller size on breast ultrasonography（P＜0.05）. Compared with similar size of breast cancer outpatients， true interval cancer cases had significantly higher proportions of malignant calcification on mammography and invasive ductal carcinoma（P＜0.05）. Among the total 110 interval breast cancer cases， only 1 case was assigned to mammography as a referral， and the referral proportion was only 0.91%. In regard to the diagnosis mammography， 53 out of 103 interval cases（48.2%） were characterized by malignant calcification. Conclusion In breast cancer screening， women with younger age are prone to interval cancer. As nearly half of the interval cancer cases contained malignant calcification on diagnostic mammography， breast cancer screening using breast ultrasonography and additional mammography may avoid part of interval cancer cases.