Although most of the microarray challenges are known and under control, the present study has an important specific challenge that is the isolation and enrichment of the circulating cancer cells. Currently, the proportion of circulating cancer cells to other nucleated blood cells (leucocytes) is unknown in patients suffering from pancreatic cancer. Therefore, the first step will be to determine the number of cancer cells per ml blood in pancreatic cancer patients and to determine the variability among different patients. A second step is to develop an enrichment method to concentrate the cancer cells without selecting specific types of cancer cells or loss of information on the initial proportion of cancer cells in each patient's blood stream. The fastest way to isolate the circulating cancer cells is using flow cytometry after density-gradient pre-enrichment in combination with negative selection strategies to discard leukocytes (CD45+ and CD34+) from the sorted 'circulating' cancer cells. Isolating cells with LCM has been used many times successfully for microarray studies. It has been reported that LCM can easily dissect several thousands of cells from pancreatic tissue with a RNA-yield of around 1ng/1000 cells (Datson NA, Meijer L, Steenbergen PJ. Morsiak MC, van der Laan S, Meijer OC, de Kloet ER. Expression profiling in laser-microdissected hippocampal subregions in rat brain reveals large subregion specific differences in expression. Eur J Neurosci 2004; 20: 2541-54. Player A, Barrett JC, Kawasaki ES. Laser capture microdissection, microarrays and the precise definition of a cancer cell. Expert Rev Mol Diagn 2004; 4: 831-40. Espina V, Geho D, Mehta AI, Petricoin EF 3rd, Liotta LA, Rosenblatt KP. Pathology of the future: molecular profiling for targeted therapy. Cancer Invest 2005; 23: 36-46. Crnogorac-Jurcevic T, Efthimiou E, Nielsen T, Loader J, Terris B, Stamp G, Baron A, Scarpa A and Lemoine NR. Expression profiling of microdissected pancreatic adenocarcinomas. Oncogene 2002; 21: 4587-4594).