Abstract P5-07-07: The immune microenvironment of ductal carcinoma in situ of the breast

Abstract

Abstract Background: The importance of tumor-infiltrating lymphocytes (TIL) in invasive breast carcinoma for tumor development and therapeutic response is widely accepted. However, the immune microenvironment of breast ductal carcinoma in situ (DCIS) has not been fully elucidated. Evasion of immune surveillance is a necessary step in tumor evolution. In DCIS, the tumor cells are relatively protected from the immune system due to an myoepithelial cell layer and basement membrane, and intraductal immune cells are rarely detected. In contrast, in invasive disease, cancer cells and immune cells are often intermingled. Thus, understanding the immune microenviroment of in situ to invasive carcinoma transition might be particularly important to identify novel targets for early stage of tumor invasion. Aims: The aim of this study is to evaluate the clinical importance of TILs in DCIS. Methods: TILs were assessed in 133 DCIS samples with or without microinvasive disease according to the proposed method from the International Immuno-Oncology Working Group on Breast Cancer. In addition, the relationship between TILs in DCIS and clinicopathological features was evaluated. Results: TILs are present in most DCIS in varying levels. The median proportion of TILs in DCIS was 14%. Only a minority of DCIS showed >50% TILs, which represented only 12.8% of all cases. High TILs in DCIS was significantly associated with comedo necrosis (p<0.0001), high nuclear grade (p=0.0030), ER negativity (p<0.0001), PR negativity (p<0.0001), HER2 positivity (p=0.0030). Triple negative DCIS and HER2 positive DCIS had significantly higher level of TILs (p=0.0008). No correlation was demonstrated between TILs and recurrence risk. Conclusions: High TILs in DCIS was significantly associated with adverse histopathologic features. Further characterization of immune environment of DCIS may be essential for immunotherapy and breast cancer prevention. Citation Format: Yamashita N, Hisamatsu Y, Shigechi T, Tokunaga E, Saeki H, Oki E, Maehara Y. The immune microenvironment of ductal carcinoma in situ of the breast [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-07-07.