Cytogenetic analysis of Circulating Tumor Cells of metastatic prostate cancer

2174 Tumor cells in blood of patients with metastatic carcinomas have been associated with poor survival prospects. In this study we evaluate the presence of cytogenetic abnormalities in Circulating Tumor Cells (CTC) detected in patients with metastatic prostate cancer. CTCs were enumerated in 7.5 mL of blood with the CellSearch System. After enumeration of the Cytokeratin+, CD45-, nucleated CTC, the fluid in the analysis cartridge was removed and the cells were fixed while maintaining their original position. Fluorescence in situ hybridization (FISH) is applied to the fixed cells labeling the centromeric regions of chromosome 1, 7, 8 and 17. After FISH the cartridges were placed on a CellTracks Analyzer equipped with a 40X objective (NA0.60). The previous identified CTCs are revisited and fluorescent images of each of the four chromosomes labels were acquired. Next, the copy number of chromosomes 1, 7, 8 and 17 were determined for each CTC. Leukocytes surrounding the CTC were used as internal controls. 61% of the blood samples taken after initiation of therapy contained ≥ 1 CTCs and FISH was applied to 84 of the CTC containing blood samples from 42 metastatic prostate cancer patients. The 84 samples contained a total of 2932 CTC (mean=5, average= 33.7, SD=76.0). Of the 2932 CTC, 225 (8%) were lost during the fixation and FISH. Of the remaining 2707 CTC no FISH signals were detected in 69% of the CTC. The lack of FISH signals in these CTC is ascribed to apoptosis as the surrounding leukocytes showed good quality FISH signals. The 829 (31%) evaluable CTC contained on average 2.8 copies of chromosome 1, 3.0 copies of chromosome 7, 3.3 copies of chromosome 8 and 2.3 copies of chromosome 17. 664/829 (80%) of the CTC were aneuploid and a higher amplification of the chromosomes 1, 7, 8 and 17 was observed with increasing CTC number. In only 1 patient no aneuploid cells were detected and this patient only had 1 CTC. Heterogeneity in the chromosomal abnormalities was observed between CTC of different patients as well as among CTC of the same patient. In the same samples 885 leukocytes were evaluated as controls and showed an average of 1.9, 2.0, 1.9 and 1.8 copies of chromosome 1, 7, 8 and 17 respectively. Cytogenetic composition of CTC can be assessed after they have been identified by the CellSearch system. The relation between the presence of aneusomy, the extent of amplification and outcome will next be investigated.