RecruitingPhase 2Drug trialSerial Circulating Tumor DNA (ctDNA) Monitoring During Adjuvant Capecitabine in Early Triple-negative Breast CancerThe purpose of the study is to evaluate the use of a circulating tumor DNA (ctDNA) assay, ie, a "liquid biopsy," as a tool to identify triple-negative breast cancer (TNBC) patients who will or will not experience benefit from treatment with capecitabine. Participants will be monitored for changes in ctDNA in the blood over time received during capecitabine treatment. Results of ctDNA analysis will be correlated to genetic characteristics of individual tumors. This may inform future clinical trials in which patients could receive a different treatment than capecitabine to reduce their risk of breast cancer relapse.