Detection and characterization of putative metastatic precursor cells in cancer patients.

Metastasis is the major cause of cancer-related death. Single disseminated tumor cells (DTC) can be detected in the bone marrow and peripheral blood years before the occurrence of clinically detectable metastases. Recent clinical studies, however, have clearly indicated that a significant fraction of breast cancer patients with DTC never develop distant metastases (1). Thus, DTC detected by sensitive immunocytochemical and molecular assays may be apoptotic or may lack stem cell properties and never give rise to an overt metastasis. The ability to detect and characterize viable DTC is therefore of utmost importance. We applied a novel technique for the detection and ex vivo characterization of single viable DTC derived from epithelial tumors. Our technique for detection of specific secreted proteins, epithelial immunospot (EPISPOT), is an adaptation of the enzyme-linked immunospot assay. EPISPOT detects only viable tumor cells and can detect protein secretion at an individual cell level, allowing the direct determination of protein-secreting cell (SC) frequencies. Immunospots are the protein fingerprint left only by the viable …