Washing solution of tissue biopsy compared with paraffin-embedded tissue for NSCLC gene test.
Authors: Wu Yuanqiang , Xiong Hui , Ma Jinan , Qiu Zhenhua , Li Zhenjiang , Quan Weini 
Published: June 2023

e21104 Background: Non-small cell lung cancer (NSCLC) is the leading cause of cancer related death, whose targeted therapy is precisely based on gene type. Gene diagnosis is as important as pathological diagnosis and driver gene mutations should be detected as soon as possible. There are generally a few sources to obtain patients’ deoxyribonucleic acid (DNA), such as paraffin tissue of tumor, cytological specimens from bronchoalveolar fluid or pleural effusion, free DNA from blood, hydrothorax, ascite, or cerebrospinal fluid. Our research aims to find out whether washing solution of lung mass biopsy in double distilled water is feasible for detecting gene mutation, and whether its gene type is consistent with that from Next Generation Sequencing (NGS) of paraffin tissue. Methods: 25 clinically diagnosed NSCLC patients from Department of Oncology, Second Xiangya Hospital, Central South University were collected. We used double distilled water to wash the CT-guided percutaneous pulmonary mass biopsy, which was processed to extract DNA. DNA samples were tested for epidermal growth factor receptor (EGFR) gene mutation by amplification refractory mutation system (ARMS)-PCR. 6 of them as well as all 25 paraffin tissue samples were tested for large panel gene mutations by NGS. The gene type consistency between washing solution and paraffin tissue was analyzed by GraphPad Prism V9.4.1. Results: 16 of 25 washing solution DNA samples tested by ARMS-PCR were EGFR mutation positive, including 9 cases of EGFR exon19 deletion, 5 cases of EGFR exon21 L858R, and 2 cases of EGFR exon21 L858R and T790M. Other 9 of 25 samples were EGFR mutation negative. 17 of 25 paraffin tissue samples tested by NGS were EGFR mutation positive, including 9 cases of EGFR exon19 deletion, 7 cases of EGFR exon21 L858R, and 1 case of EGFR exon21 L858R with T790M. There was one washing solution sample showed no EGFR mutation while its tissue sample showed EGFR exon21 L858R. Compared to NGS on paraffin tissue, the sensibility of ARMS-PCR on washing solution was 94.1%. The specificity was 100%, positive predictive value was 100%, negative predictive value was 88.9%, accuracy rate was 96.0%, misdiagnosis rate was 0, and omission diagnostic rate was 5.9%. EGFR types of 6 washing solution samples tested by NGS were exactly the same as that by ARMS-PCR and that of paraffin tissue samples by NGS. The time to obtain gene result was significantly different. ARMS-PCR of washing solution took 1 day, NGS of washing solution took around 7 days, while pathological examination and NGS of paraffin-embedded tissue took around 14 days. Conclusions: The washing solution of CT-guided percutaneous lung mass biopsy in double distilled water is feasible to obtain EGFR type rapidly and efficiently for NSCLC. It is the fastest method to get patients’ gene type at present. Thus, the washing solution of biopsy could be a new DNA source for NSCLC gene test and making decision on targeted therapy ahead of time.