Cell HE staining smears and paired cell paraffin sections in detection of epithelial growth factor receptor gene of pleural fluid specimens.

OBJECTIVES

The advanced non-small cell lung cancer (NSCLC) patients with pleural effusion have no opportunity for surgery treatment. Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are the first-line drugs for these patients with -sensitive mutation. However, the disease progression and drug update during or after treatment of EGFR-TKIs bring more challenges and puzzles to clinical diagnosis and treatment, which inevitably requires archived pleural cell samples for EGFR re-examination or comparative study. Understanding the DNA quality of archived pleural fluid samples and effectively using archival data of pleural fluid cells are of great significance for tracing the origin of cases and basic medical research. This study aims to evaluate the consistency of EGFR mutant gene expression between the 2 methods, and to explore a reliable way for preserving cytological data and making full use of cytological archival data via cell HE staining smear and cell paraffin section.

METHODS

A total of 57 pleural fluid cytology cases in the Department of Pathology of China Aerospace Center Hospital from October 2014 to April 2021 were selected. Tumor cells were detected by cell HE staining smears and immunohistochemical staining for TTF-1 and Napsin A in the paired cell paraffin sections. There were more than 200 tumor cells in cell HE staining smear and the proportion of tumor cells were ≥70% in matched cell paraffin sections. Patients with 2 cell smears (one for cell data retention and the other for DNA extraction) were selected as the research subjects, and 57 pleural fluid samples were enrolled. gene mutation was detected by amplification refractory mutation system-polymerase chain reaction in 57 paired cell HE staining smears and cell paraffin sections. DNA concentration was 2 ng/μL. Cell HE smear was amplified side-by-side with DNA samples from paired cell paraffin sections. Result determination was according to the requirements of the reagent instructions. The external control cycle threshold (Ct) value of the No. 8 well of the samples to be tested was between 13 and 21, which was considered as successful and reliable samples. When the Ct value of gene mutation was <26, it was considered as positive; when the Ct value was between 26 and 29, it was critical positive; when the Ct value was equal or more than 29, it was negative. ΔCt value was the difference between mutant Ct value and externally controlled Ct value. The smaller the ΔCt value was, the better the quality of DNA of the detected sample was.

RESULTS

Among the 57 pleural effusion samples, 42 patients were hospitalized with pleural effusion as the first symptom, accounting for 73.7% (42/57). mutation was detected in 37 samples [64.9% (37/57)]. The mutation rate for was 37.8% (14/37) while for was 48.6% (18/37). Females were 56.7% (21/37) of mutation cases. The mutation consistency rate of cell HE staining smear and matched cell paraffin sections was 100%. The ΔCt values of cell HE staining smears were less than those of matched cell paraffin sections. The mutation Ct values of 37 cytological samples were statistically analyzed according to the preservation periods of the years of 2014-2015, 2016-2017, 2018-2019, and 2020-2021. There were significant differences in cell paraffin section in the years of 2014-2015 and 2016-2017 compared with the years of 2018-2019 and 2020-2021, while no significant differences were found in cell HE staining smear. Statistical analysis of externally controlled Ct values of 57 cytological samples showed that there were significant differences between cell HE staining smears and cell paraffin section in the years of 2014-2015 and 2016-2017, compared with the years of 2018-2019 and 2020-2021. The mutational Ct values of 37 paired cell blocks and smears were all <26, and the externally controlled Ct values of 57 paired cell paraffin sections and HE staining smears were all between 13 and 21.

CONCLUSIONS

The DNA quality of cell HE smears and matched cell paraffin section met the qualified requirements. Two methods possess show an excellent consistency in detecting mutation in NSCLC pleural fluid samples. The DNA quality of cell HE staining smear is better than that of cell paraffin sections, so cell HE staining smear can be used as important supplement of the gene test source. It should be noted that the limitation of cell HE staining smears is non-reproducibility, so multiple smears of pleural fluid are recommended to be prepared for multiple tests.