A new approach to phenotyping disseminated tumor cells: methodological advances and clinical implications

At the time of primary therapy (surgery, systemic chemotherapy and/or radiation), disseminated tumor cells in the bone marrow can be found in almost one-third of patients with cancer of the breast, ovary, esophagus, stomach, colon, and other solid tumors. Whereas the prognostic impact of the mere presence of these cells is still a matter of debate, it has been shown that expression of tumor-associated antigens in disseminated tumor cells is linked to more aggressive disease. Therefore, further characterization of disseminated tumor cells at the protein and gene level has become increasingly important. To date, the most common detection method for disseminated tumor cells in the bone marrow is an immunocytochemical approach using cytokeratin-directed antibodies for detection of epithelial cells and the APAAP system for their visualization. We have established a new double immunofluorescence technique enabling simultaneous detection, phenotyping, and antigen quantification of disseminated tumor cells. Mononuclear cells from bone marrow are enriched by Ficoll gradient centrifugation and cytospins are prepared. Double immunofluorescence is performed using antibodies against cytokeratins 8/18/19 (mAb A45B/B3) and the uPA receptor CD87 (pAb HU277). CD87 expression is recorded by confocal laser scanning microscopy (CLSM) using fluorescence labeled latex beads as the reference; staining intensities of all the scans are then summed and quantified (extended focus). This protocol, originally designed for disseminated tumor cells in bone marrow, can also be applied to disseminated tumor cells in blood, to leukapheresis cells or to cells present in malignant ascites or other malignant effusions. The tumor cells detected may be used for gene and mRNA analyses. Furthermore, disseminated tumor cells also represent interesting targets for clinical studies on patient prognosis or prediction of therapy response as well as for specific tumor-biological therapies.