[Analysis of the Relationship Between the Quality of Small Biopsy Specimens of 
Non-small Cell Lung Cancer and the Mutation Rate of EGFR Gene].

backgroundEpidermal growth factor receptor (EGFR) is the gene with the highest mutation rate in non-small cell lung cancer (NSCLC) patients, and the accurate evaluation of its mutational status can facilitate patients receiving targeted drug therapy and thereby prolong patients' survival. The gene testing platform has adequacy requirements for the specimen quality in order to obtain accurate examination results. It has been reported that the number and proportion of tumor cells in samples will affect the detection rate of EGFR gene mutation. The present study aims to analyze the relationship between the quality of small biopsy specimens of NSCLC and the mutation rate of EGFR gene with amplification refractory mutation system (ARSM) test.

methodsAfter collecting the clinical characteristics of 299 cases small biopsy of lung adenocarcinoma, DNA concentration of the specimens and the mutational status of EGFR gene, the number and proportion of tumor cells in HE stained sections evaluated using light microscopy, the relationship between specimen quality and the mutation rate of EGFR gene were analyzed.

resultsThe mutation rates of EGFR for the groups with tumor cell number ≤500 and >500 were 40.7% (11/27) and 43.8% (119/272) respectively, without significant difference (P=0.764). The mutation rates for the groups with DNA concentration ≤20.4 ng/μL and >20.4 ng/μL were 42.7% (64/150) and 44.3% (66/149) respectively, without significant difference (P=0.776). The mutation rates for the groups with tumor cells proportion ≤30% and >30% were 29.4% (20/68) and 47.6% (110/231) respectively, demonstrating significant difference (P=0.008). Multivariate Logistic analysis showed that male, thyroid transcription factor-1 (TTF-1) negative, smoking history and tumor cell proportion less than 30% were main factors that contributes to the low detection rate of EGFR gene mutation.

conclusionsAfter meeting the minimum requirements for detection, the EGFR mutation rate is affected by the proportion of tumor cells in the sample. Therefore, it is necessary to re-evaluate the tumor cell proportion in the last section after the genetic test section. For samples with lower tumor cell proportion, enriching tumor cells through microdissection and other methods is recommended for a more accurate detection result. For specimens that cannot be enriched with tumor cells, circulating tumor DNA (ctDNA) test can be performed as a supplement. If the result is still negative, another biopsy should be considered to obtain enough tumor specimens for molecular testing.