Comparison of two techniques for the screening of human tumor cells in mouse blood: Quantitative real-time polymerase chain reaction (qRT-PCR) versus laser scanning cytometry (LSC).

The formation of metastases is often investigated in xenografted human tumors in mice and the need arises to detect disseminated human tumor cells in small volumes of mouse blood. Two techniques, namely quantitative real-time polymerase chain reaction (qRT-PCR) and laser scanning cytometry (LSC), were compared for screening of 100mul blood samples from immunodeficient mice spiked with a defined number of human HT29 colon carcinoma cells. With both techniques (qRT-PCR for amplifying of human Alu-sequences and LSC techniques for screening of fluorescence labelled cells), it was possible to detect single disseminated human tumor cells. Using the qRT-PCR technique, a recovery rate of nearly 100% was found when 10-10000 cells were added to 100mul blood. In contrast, the median recovery rate of the LSC technique varied between 20% (10cells/100mul blood) and 7.5% (10000cells/100mul blood). Thus, it is advisable to quantify the number of human tumor cells in mouse blood by qRT-PCR and to use LSC for phenotyping of disseminated tumor cells only.