Background

Malignant pleural effusion (MPE), also known as pleural effusion, is a pleural effusion caused by the metastasis of malignant tumors originating in the pleura or other malignant tumors involving the pleura. Almost all malignant tumors can invade the pleura and produce MPE, which is more common in lung cancer, breast cancer, gastrointestinal cancer and other cancers^[1].

Malignant cells in pleural effusion and/or pleural tissue are the "gold standard" for the diagnosis of MPE. The study reported that the sensitivity of pleural effusion cytology in the diagnosis of MPE was 60.0% (40.0%~87.0%)^[2,3]. Its diagnostic performance depends on the location of the tumor. If it is located on the surface of pleural mesothelial cells, malignant cells are easy to fall off and enter pleural effusion. Only a few malignant cells will fall off into the pleural space when they are located at or below the serous layer. The minimum amount of fluid required for cytopathological examination is still controversial. It is generally considered that 20~50 ml is enough. However, it is reported in the literature that the amount of fluid submitted for examination>75 ml can improve the diagnostic rate of MPE^[4].

Study of pleural fluid cell samples in gene detection

1.In 2019, the study[5]of Peking University Cancer Hospital retrospectively collected 295 MPE samples from patients with lung adenocarcinoma.92 patients had matched tissue and plasma samples, and 248 patients had plasma samples. The consistency between the detection of malignant pleural effusion cells and tissue detection was 87.1%. The sensitivity and specificity of EGFR mutation detection of pleural effusion cells were 71.4% and 96.5%, which could better reflect the EGFR mutation of tumor tissue and effectively guide the targeted treatment of patients.

Comparison of EGFR mutation detection results between MPE and tissue

2.The Expert Consensus on Detection of EGFR T790M Gene Mutation in Chinese Patients with Non-small Cell Lung Cancer^[6]points out that when tissues cannot be obtained, other samples such as tumor cytology samples or plasma samples can be considered for EGFR T790M detection (Category 2A).

Gene detection of pleural effusion supernatant samples

1.One study^[7]included 63 patients with metastatic lung cancer (n=30, cohort 1) or no matched tumor tissue (n=33, cohort 2).PE and plasma samples were collected from each patient at the same time. The supernatant and cell sediment of PE were treated respectively to extract cfDNA (PE cfDNA) and sediment DNA (sDNA). The results showed that 98.4% (62/63) of PE cfDNA samples in all patients had detectable somatic changes, while 90.5% (57/63) of PE sDNA and 87% (55/63) of plasma cfDNA. That is to say, the ctDNA content in the supernatant of pleural effusion is much higher than that of pleural effusion sediment cells, and has a higher mutation detection rate and higher mutation detection abundance: pleural effusion supernatant (98.4%)>pleural effusion cells (90.5%).

Variation detection of all patients

2.Another study^[8]used the second generation sequencing (NGS) method to detect the gene mutation in the pleural fluid supernatant of lung adenocarcinoma patients (n=150).All 150 samples obtained enough DNA, and 104 (90%) of 116 samples were successfully tested for NGS. Somatic mutations were detected in 82% of the samples and clinically relevant mutations were found in 50% of the patients. The comparison of operable driving mutations detected in supernatant and plasma samples showed 84% consistency.

Conclusion: Molecular gene detection of pleural effusion supernatant makes routine gene detection convenient. It is highly rich in fresh tumor DNA, which can provide valuable samples for lung cancer gene detection. Especially for patients with insufficient tumor tissue, it can reduce the failure rate of gene detection, shorten the detection cycle, and avoid repeated biopsy.

Overlap of clinically relevant operable driving mutations detected between FNA supernatant samples and corresponding plasma cfDNA liquid biopsy detection

Sample submission for inspection

For sample submission, pleural effusion is stored in a 50mL centrifuge tube, 30-50mL for tumor multi gene project, 15-20mL for EGFR project, and transported at low temperature.

In Recommendation 6 of the Chinese Expert Consensus[9]on pleural effusion diagnosis, it is pointed out that for non-small cell lung cancer with MPE, tumor tissue samples or pleural effusion sediment cell mass samples can be selected for detection.

Although hydrothorax samples play a highly consistent detection performance with tissue samples in tumor gene detection.However, it is undeniable that the detection rate of surgical or puncture samples at the tumor site is better than that of pleural effusion cells or supernatant samples.Therefore, in terms of sample selection, the Chinese expert consensus on the clinical application of second-generation sequencing technology in NSCLC still recommends that tumor patients' gene testing should be the first choice for tissue testing. In the case of insufficient tissue samples or inaccessible tissues, liquid biopsy can be selected as a supplementary means^[10].

Key points of Chinese experts' consensus on the clinical application of second-generation sequencing technology in NSCLC

For Feishuo biological lung cancer related projects, such as human EGFR/KRAS/BRAF/HER2/ALK/ROS1 gene mutation detection kit (GXZZ 20203400094) and human EGFR gene mutation detection kit (GXZZ 20193400366), pleural effusion extraction and precipitation cell samples can be used for detection. For details, please contact to discuss cooperation matters.

Reference

[1]Medicina (Kaunas). 2019 Aug 15;55(8):490.

[2]DOI: 10.1136/thx.2010.136978.

[3]Can Respir J, 2020, 2020: 2950751.

[4]Cancer Cytopathol, 2014, 122(9): 657‐665.

[5]Lung Cancer. 2019 Sep;135:116-122.

[6]Expert consensus on detection of EGFR T790M gene mutation in Chinese patients with non-small cell lung cancer

[7]Theranostics 2019; 9(19): 5532-5541.

[8]Annals of Oncology 30: 963–969, 2019

[9]Chinese Expert Consensus on Diagnosis of Pleural Effusion

[10]Chinese expert consensus on the clinical application of second-generation sequencing technology in NSCLC (2020 version)