Bone Marrow Micrometastases and Circulating Tumor Cells

In clinical practice, although local recurrence or distant metastasis develops in some individuals who have been assessed as low risk despite treatment, some individuals with high-risk disease do not relapse despite systemic and local therapy. Therefore, oncologists need to determine objective prognostic factors to identify early recurrence and metastasis in patients with breast cancer. Based on the presumption of residual disease, clinicians have recently tried to identify micrometastases by using disseminated tumor cells (DTCs) in the bone marrow and circulating tumor cells (CTCs) from the peripheral blood. However, identifying the presence of DTCs and CTCs has required experienced staff and special laboratory. DTCs are known as epithelial cells in the bone marrow, and they are also considered micrometastases in the bone marrow. The morphological characteristics of DTCs include large cells with a large nucleus, nuclear granulation or stippling, strong or irregular staining for cytokeratin, and cytokeratin filaments. DTCs are observed in approximately 30% of early-stage breast cancer patients. Tumor cells circulating in the peripheral blood of patients with cancer are called CTCs. CTCs are cells that have entered the peripheral blood circulation after having detached from an existing primary tumor or its metastases. DTCs and CTCs can be used to predict progression-free and overall survival as well as response to treatment.