Circulating tumor cell clusters in the peripheral blood of colorectal cancer patients. 
Recently several reverse transcription-PCR techniques have been proven to be useful for the detection of circulating micrometastases.  However, this way intact cell clusters that were found in animal experiments of prognostic value could not be detected.  In this study, evaluation and modification of a commercial, cytokeratin-based, immunomagnetic cell separation method was performed for the detection of intact cell clusters in colorectal carcinoma patients.  Thirty-two colon cancer patients (6 were in Dukes stage B, 13 in stage C, and 13 in stage D) and 20 healthy donor samples were evaluated.  Immunomagnetic cell separation was performed from the buffy coat of peripheral blood samples (20 ml) using the Carcinoma Cell Enrichment Kit (Miltenyi Biotec, Bergisch Gladbach, Germany), avoiding any filtering steps.  The enriched cell fraction was cytocentrifuged and immunocytochemically labeled using a pancytokeratin antibody (MNF116; Dako).  Of 20 healthy samples, 2 contained one cytokeratin-positive cell.  Of 32 single samples from malignant cases, 24 showed cytokeratin-positive cells.  Tumor cell clusters, mixed-cell doublets (one cytokeratin-positive and -negative cell), and mixed-cell clusters were detected in 22 of 24 patients.  In six cases, cytokeratin-positive dendritic-like cells were detected.  Follow-up data indicate that chemotherapy cannot destroy all of the circulating tumor cell clusters.  Using the methods presented, we could detect circulating colon cancer cells and cell clusters in colon carcinoma patients.  Similar cellular structures were described previously only in rats.  Present data prove that such structures are present in human colorectal cancer, too.