Table 2.

Comparison of different body fluid samples.

Body fluid type	Main biopsy components	Advantage	Challenge
Blood	CTC, ctDNA, exosome	Mature analysis method. Tumor progression can be monitored in real-time. For the most frequent patients. It is used more commonly and widely used	High false negative rate. Low biomarker quality and quantity. Biomarkers have a shorter half-life. Can’t collect continuously
Urine	CTC,ctDNA, Urine-mRNA, exosome	The sample size is large. Non-invasive, and can be collected continuously. Suitable for longitudinal follow-up. There was a higher response to the tumor metastasis	The collection process is susceptible to contamination. The number was decreased after kidney filtration
Saliva	Saliva-mRNA, miRNA	Non-invasive operation. Low risk of cross-contamination. Lung cancer progression can be monitored in real-time.	Sample size is less. Low biomarker quality and quantity. Complex components, including enzymes, antibodies, hormones, etc
Bronchoalveolar lavage fluid	Tumor cell BALF-mRNA, miRNA, lncRNA, exosome	Non-invasive operation. Early-stage central lung cancer has a high sensitivity and specificity. Intratumoral heterogeneity. The sample size is large	Sample size is less. Lack of mature sampling methods
Pleural effusion	CTC, ctDNA, PE-mRNA	High quality and quantity of the biomarkers. Highly correlated with the clinical characteristics	Invasive operation. Lung cancer progression cannot be monitored in real-time. Early-stage patients are not applicable