Abstract P6-02-06: Ductal carcinoma in situ and breast cancer screening in Japanese breast cancer registry
Authors: Iwamoto T , Kumamaru H , Miyata H , Tomotaki A , Niikura N , Kawai M , Anan K , Hayashi N , Masuda S , Tsugawa K , Aogi K , Ishida T , Masuoka H , Iijima K , Matsuoka J , Doihara H , Kinoshita T , Nakamura S , Tokuda Y 
Published: May 2016

Abstract
Background: There is an increasing trend in the rate of breast cancer screening for women in all ages in Japan. While screening leads to early cancer detection and improved treatment outcome, it may lead to over-treatment of potentially benign tumors. Little is known about the biological differences between screen- and self-detected cancers.
Method : To compare the biological characteristics of breast cancers by the mode of detection, we used the data from Japanese Breast Cancer Registry (JBCR), a nation-wide registry of newly diagnosed breast cancer cases in Japan. We enrolled into the study cohort female patients who underwent surgical resection of their breast cancers during the period between January 1st 2004 and December 31st 2011, whose mode of cancer detection were recorded in the registry. We compared the clinico-pathological features of the tumors including histological classifications, estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) status, and TNM stages between screen- and self-detected cases. Also, we assessed the yearly trend in the proportion of screen-detected cases over the study period.
Results: We identified 205,544 patients matching the inclusion criteria within the registry. In total, 31.8% (65,358 / 205,544) of cases were detected by screening. Cases detected by screening were more likely to have favorable prognostic features than those self-detected: (DCIS: screening 19.8% vs self-detection 4.1%, node negative: 77.0% vs 61.6% and ER positive: 82.0% vs 72.9%, respectively). On the contrary, self-detected tumors were more likely to have poor prognostic characteristic (HER2 positive: screening 11.7% vs self-detection 14.0%, T3 or T4: 2.1% vs 9.8, respectively). All these findings reached statistical significance (p-value &lt; .001). Over the years, the proportion of breast cancers detected by screening among all cases increased from 21.7% in 2004 to 37.1% in 2011. During the same time period, among the all treated DCIS, the proportion of screen-detected DCIS increased from 41.5% to 66.0% and that of ER positive cancers also increased from 23.2% to 39.7%.
Interpretation:
This study using JBCR demonstrated that DCIS tumors account for a substantial proportion of screen-detected cancers. The distributions of biological characteristics in screen-detected cancers differ from those observed in self-detected cancers. This may account in part for the favorable prognostics of screen-detected cases.
Citation Format: Iwamoto T, Kumamaru H, Miyata H, Tomotaki A, Niikura N, Kawai M, Anan K, Hayashi N, Masuda S, Tsugawa K, Aogi K, Ishida T, Masuoka H, Iijima K, Matsuoka J, Doihara H, Kinoshita T, Nakamura S, Tokuda Y. Ductal carcinoma in situ and breast cancer screening in Japanese breast cancer registry. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-02-06.