OBJECTIVETo establish a quantitative method to detect circulating tumor cells (CTC) in patients with small cell lung cancer, and analyze its sensitivity and stability.

METHODSA specific primer and probe for prepro-gastrin-releasing peptide (preproGRP) was designed and a quantitative RT-PCR method was established to detect preproGRP mRNA. Cell incorporation method was used to evaluate the sensitivity. Magnetic cell sorting (MACS) was used to isolate and purify CTC from peripheral blood, and the MACS in combination with morphological diagnosis were used for cell counting.

RESULTSThe isolation rate of CTC by MACS was 30% and the lower detection limit was 5 cells per ml blood. The sensitivity of quantitative RT-PCR in detection of preproGRP mRNA in CTC was 0.64 cells per reaction, and the lower detection limit was 50 cells per ml blood, which was lower than that of MACS. However, the cell numbers calculated by Ct value was in greater accordance (about 80%) with actual cell numbers than that obtained by MACS.

CONCLUSIONSPreproGRP quantitative RT-PCR and MACS have both advantages and disadvantages in detecting CTC of SCLC patients. MACS has a higher sensitivity, and is more favorable when CTC count is below 50 per ml blood. Meanwhile, preproGRP mRNA quantitative RT-PCR is more reliable in calculating actual cell numbers.