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Detection of Circulating Tumour Cells for Cancer Therapy Monitoring Cancer is a leading cause of death worldwide, with more than 7.6 million deaths in 2007 [1]. Singapore is tackling the disease upfront with major initiatives, including a translational clinical research flagship programme (TCR), the Singapore Gastric Cancer Consortium (SGCC). This particular cancer is the second most common cause of cancer deaths worldwide, with 600 new cases diagnosed each year in Singapore [2]. During discussions with the scientists and clinicians from SGCC, it appeared that the clinicians lack precise tools to be able to tailor dosage of treatments usually laden with potentially serious side effects (radiation, chemotherapies). For example, imaging techniques and biopsies can only detect tumours that have reached a certain size; hence it may be difficult to establish the complete remission of the disease. Moreover these techniques can be painfully invasive or costly. In 2008, the United States Food and Drug Administration (FDA) cleared the way for a system (CellSearch™, Veridex) which reports the level of circulating tumour cells (CTCs) in metastatic breast cancer patients. CTCs are tumour cells that have detached from the primary tumour site and are circulating in the blood stream. Their number is a clear indicator of the aggressiveness of the cancer as well as the efficacy of the therapy being applied [3]. In collaboration with SGCC, IME is developing an integrated microsystem for the detection of CTCs from whole blood that would help doctors in their therapeutic decisions. The detection of CTCs is usually based on the presence of the specific epithelial marker EpCAM on their surface. The technical challenge lies with the fact that only a few such cells can be found in millilitres of blood, amongst millions of white blood cells and billions of red blood cells, even for patients at an advanced stage, who would present an increased number of CTCs. Conventionally, the purification is performed via complex magnetic separation steps in tubes, using beads coated with an antibody specific to the EpCAM receptor. The nature of the cells is then confirmed via fluorescent staining of cancer markers (cytokeratins) and lymphocytes receptors (CD45 for example) [4]. The CellSearch™ system has automated this procedure into a reproducible assay. However the procedure still requires a sample transfer between two separate machines. Besides, the sample even after magnetic purification still contains a lot of other cells, necessitating a labour-intensive manual inspection of the stained cells by a trained specialist to establish their CTC nature. Hence the test is complex and costly. Acknowledging this problem, the IME team is developing an integrated solution, combining enrichment and label free detection in the same module in order to minimise cell loss and improve throughput. The cells are enriched (isolated) directly from whole blood by immunomagnetic separation in a microfluidic chamber, followed by single cell precision counting of cells using the label free electrical impedance detection technique in the same chamber without sample transfer. The sensor under development is designed to detect a wide range of cell numbers between 0 and 5000 with single cell precision. The ability to detect such a wide range of cell numbers with such precision allows this technology to be used in prognostics, early diagnosis and therapy monitoring. The team is now working on a system prototype, with the aim to process up to 2 ml of blood in a fully automated manner. Following prototyping, clinical trials will begin in collaboration with SGCC using samples from gastric cancer patients. The estimated cost of the instrument prototype is SGD $50,000, with an estimated per test cost of <SGD $100. Comparatively, the clinically approved CTC method is priced at about USD $650 (approximately SGD $910). Cancer is rated the number two killer in Singapore. From 2002 to 2006, there were 42,424 incidents of cancer diagnosed among the residents of Singapore [6]. References
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