Breast cancer is the most commonly diagnosed type of cancer among females worldwide. It is also the leading cause of female cancer-related death in developing countries. Though novel biomarkers and new strategies for diagnosis, monitoring course of disease, and treatment of breast cancer have been found, these methods are invasive, costly, labor-intensive, and inadequate to fully gauge treatment response and disease recurrence. Therefore, novel biomarkers with greater sensitivity and specificity, and which are easy to perform are needed in breast cancer oncology. There is growing interest in the potential use of circulating tumor cells and circulating tumor deoxyribonucleic acid fragments in liquid biopsy as non-invasive biopsy materials for early detection of breast cancer, monitoring disease progression, and understanding reasons for treatment resistance. This review is a discussion of current status of utilization of these liquid biopsy materials in breast oncology.