Background: Triple negative breast cancer (TNBC), lack of ER, PR and HER2 expression, is known to have aggressive clinical features such as early recurrence, drug resistance, and frequent distant metastasis at the diagnosis. The most effective chemotherapy combinations used for early TNBC include anthracycline, taxanes, and/or platinum agents. Achieving a pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC) provides important prognostic information and is considered as a surrogate endpoint in many clinical trials especially with TNBC. Patients with residual invasive disease after NAC have a high risk for early relapse and worse prognosis compared to those with pCR. Therefore, patients who did not get pCR could be better candidates for additional adjuvant treatment because their risk of recurrence would be higher than those with pCR. The CREATE-X (capecitabine for residual cancer as adjuvant therapy) trial howed that adjuvant capecitabine treatment improved 5-yr rate of disease free survival in TNBC subtype. A recent study indicated that immunosuppressive microenvironment had developed even in early stage of TNBC with increased T cells with a high exhaustion signature which are targets of immune modulating agents. Therefore, earlier cooperation of immune modulating drugs would be beneficial by generating a long-lasting anti-tumor immune response to micrometastatic disease, thus preventing disease relapse or recurrence. Methods: This study is a phase II, multicenter, randomized open label trial of atezolizumab (anti-PD-L1 antibody) and capecitabine compared with capecitabine in patients with TNBC who had residual disease after NAC. 284 patients will be enrolled from 15 sites in Korea with a primary objective to access the 5-yr invasive disease-free survival (IDFS) rate. Secondary objectives include 5-yr IDFS rate in PD-L1 positive population, distant relapse free survival (DRFS), overall survival (OS), and safety. Major inclusion and exclusion criteria are followings; 1) histologically confirmed TNBC, 2) received anthracycline and taxane based NAC followed by complete breast surgery, 3) residual disease after NAC must be ≥1cm in the greatest dimension, and/or have macroscopically positive lymph nodes. The study is open with 13 patients enrolled at the time of submission. Clinical trial information: NCT03756298.