Circulating Tumor Cells
Circulating tumor cells are neoplastic cells that are passively shed or actively intravasate into circulation from primary tumors and/or metastatic deposits. (47). The number of CTCs in cancer patients correlate with treatment outcome and overall survival (48). The DNA, RNA and protein content of CTCs can be evaluated for molecular characterization informative of native tumor tissue (49). CTCs constitute a small fraction of cells in circulation-1 in 109 cells (50) and thus various techniques using distinct biological and physical properties of CTCs are used to differentiate and isolate them from leucocytes, erythrocytes and other cells in a blood sample. The predominant method of CTC isolation involves enrichment for cells with EPCAM expression and lack of CD45 expression (51,52,53). This is not applicable to circulating DLBCL cells and cells from other hematological malignancies which express CD45 and lack EpCAM expression. In addition, the low abundance of CTCs makes their use in early stage of disease challenging. Other challenges with use of CTC as liquid biopsy is the need for prompt processing of whole blood after collection in most isolation platforms (54) precluding the potential for biobanking specimens for future analyses or use of archival biobanked specimens for studies.