Mammography Screening and the Incidence of Interval Cancer in Taiwan: A Single Institute’s Experience

Abstract Background/aim: Breast cancer is the most common female malignancy in the world. Nearly ninety percent of screen-detected breast cancer were diagnosed with stages 0 to II in Taiwan. Identifying breast cancer through screening can achieve early diagnosis and treatment for preventive medicine while the risk of interval cancer remains, which has unfavorable tumor characteristics and worse outcomes. The purpose of this study was to explore the effectiveness of mammography screening and the incidence of interval cancer using administration data, cancer registry and chart reviews.Materials and methods: Mammography examinations with BI-RADS (breast imaging-reporting and data system) classification were extracted from the health information system and linked to cancer registry. Targeted populations were those attending the first mammography between 2012 and 2016, while subjects with previous breast cancer, missing or incomplete data were excluded. We compared the treatment outcomes of breast cancer patients with and without mammography screening, and the incidence of interval breast cancer was estimated.Results: The total of 84,246 screening mammography and 61,230 diagnostic mammography sessions were performed from 2010 to 2020. More positive results (BIRADS 0, 3, 4 and 5) were observed for those attending the first diagnostic than the first screening mammography (43.58% versus 16.12%, p<0.001). Among 26,103 mammography screening invitees from 2012 to 2016, 325 breast cancers were ascertained from cancer registry. Of these, 234 had one, 72 had two and 19 had three episodes of mammography before cancer diagnosis, with an interval cancer rate of 0.065% estimated. The proportion of contamination from symptomatic cases, screening-detected cancers, interval cancers and cancers with delayed biopsy or confirmatory image examinations in the screening group were 29.9%, 57.5%, 5.2%, and 7.4%, respectively. Earlier stage distribution (tumor less than 2 cm without regional lymph node invasion, stage 0-I) (92% versus 81%, p<0.0001), better survivorship (96.91% versus 92.17%, p=0.007) and favorable tumor characteristics such as a lower HER2 (human epidermal growth factor receptor II) positive status and lower tumor grade (p=0.0006 and 0.012 respectively) were noted in screening-detected breast cancers.Conclusion: The effectiveness of mammography screening was ascertained in Taiwan despite high contamination from symptomatic women from this study. To improve the outcomes further with earlier detection and decrease the risk of interval cancer, the impact of repeated mammography and removal of clinical cases from screening programs should be considered.