The study describes the development and application of a microfluidic device, the 'CTC-chip,' for the efficient and selective isolation of viable circulating tumor cells (CTCs) from peripheral blood samples. The CTC-chip uses antibody-coated microposts to capture CTCs under controlled laminar flow conditions, without the need for pre-labelling or processing of samples. The device successfully identified CTCs in 115 out of 116 (99%) patient samples from various epithelial cancers, with a range of 5 to 1,281 CTCs per ml and approximately 50% purity. The CTC-chip also showed high sensitivity and specificity, and its ability to monitor changes in CTC numbers correlated reasonably well with clinical disease progression in a small cohort of patients undergoing anti-cancer therapy. The CTC-chip provides a powerful tool for accurate identification and measurement of CTCs, with broad implications for advancing cancer biology and clinical management.The study describes the development and application of a microfluidic device, the 'CTC-chip,' for the efficient and selective isolation of viable circulating tumor cells (CTCs) from peripheral blood samples. The CTC-chip uses antibody-coated microposts to capture CTCs under controlled laminar flow conditions, without the need for pre-labelling or processing of samples. The device successfully identified CTCs in 115 out of 116 (99%) patient samples from various epithelial cancers, with a range of 5 to 1,281 CTCs per ml and approximately 50% purity. The CTC-chip also showed high sensitivity and specificity, and its ability to monitor changes in CTC numbers correlated reasonably well with clinical disease progression in a small cohort of patients undergoing anti-cancer therapy. The CTC-chip provides a powerful tool for accurate identification and measurement of CTCs, with broad implications for advancing cancer biology and clinical management.