The present invention provides a method for diagnosing cancer, predicting a disease outcome or response to therapy in a patient sample. The method involves isolating a circulating tumor cell (CTC), for example, a viable CTC, from a sample using a parylene microfilter device comprising a membrane filter having or consisting of a parylene substrate, which has an array of holes with a predetermined shape and size; and detecting and quantifying telomerase activity in blood circulating tumor cells. The invention further provides methods of using cells live-captured in various applications.