Purpose: Our previous study demonstrated that cytological specimens can be used as alternative samples for detecting anaplastic lymphoma kinase (ALK ) fusion with the method of reverse transcriptase PCR (RT-PCR) in patients with advanced non-small-cell lung cancer (NSCLC). The current study aimed to investigate the feasibility of cytological specimens for ROS proto-oncogene 1, receptor tyrosine kinase (ROS1 ) fusion detection by RT-PCR in advanced NSCLC patients.
Patients and methods: A total of 2,538 patients with advanced NSCLC, including 2,101 patients with cytological specimens and 437 patients with tumor tissues, were included in this study. All patients were screened for ROS1  fusion status by RT-PCR. The efficacy of crizotinib treatment was evaluated in ROS1  fusion-positive NSCLC patients.
Results: Among 2,101 patients with cytological specimens, the average concentration of RNA acquired from cytological specimens was 47.68 ng/µL (95% CI, 43.24–52.62), which was lower than the average of 66.54 ng/µL (95% CI, 57.18–76.60, P =0.001) obtained from 437 tumor tissues. Fifty-five patients harbored ROS1  fusion gene that was detected by RT-PCR, and 14 of them were treated with crizotinib. The incidence of ROS1  fusion was 1.95% (41/2,101) in 2,101 patients with cytological specimens, similar to the rate of 3.20% (14/437, P =0.102) for the 437 patients with tumor tissue. Regarding crizotinib treatment, no statistically significant differences were observed in the objective response rate (ORR) (81.8% vs 100%, P =0.604) between the cytological and tissue subgroups of ROS1 -positive patients.
Conclusion: This study shows that cytological specimens can be utilized as alternative samples for ROS1  fusion detection by RT-PCR in advanced NSCLC patients.
Keywords: non-small-cell lung cancer, ROS proto-oncogene 1 receptor tyrosine kinase, ROS1 , cytological specimens, reverse transcriptase polymerase chain reaction, RT-PCR, crizotinib