A repeatable method for detecting circulating tumor cells in vitro is provided. The method involves combining a test sample from a patient suspected of having circulating tumor cells, and a non-lytic adenoviral system, and culture media for the cells. The adenoviral system utilizes (i) a first replication-defective adenoviral particle in which an expression cassette is packaged, said expression cassette comprising an adenoviral 5′ and 3′ ITRs and a tumor-specific promoter; and (ii) a coding sequence for a reporter protein which is expressed in the presence of circulating tumor cells, and an adenoviral 3′ ITR. The test sample and the non-lytic adenoviral system are incubated for a sufficient time to permit expression of the reporter protein, and measuring reporter protein expression in the test samples, whereby presence of reporter expression indicates the presence of circulating tumor cells in the sample. Because the system is non-lytic, the testing can be repeated on the cells which remain viable in culture. Also provided is a method for enriching test samples having circulating tumor cells and a microfluidics device suitable for CTC-specification identification and enumeration.