Table 1.

Suitability of various molecular sources for developing liquid biopsy biomarkers in cancer.

Type	Abundance	Stability	Tissue specificity	Functional info availability	Comprehensive profiling feasibility	Present in EV	Published studies*
RNA
Non-coding RNA
miRNA	High	High	Intermediate	intermediate	High	High	High (1420)
lncRNA	Low	Low	Unclear	Low	Low	Intermediate	Low (135)
Circular RNA	Low	High	Unclear	Low	Low	Low	Low (29)
piRNA	High	High	Unclear	Low	High	High	Low (8)
tRNA	High	High	Unclear	Low	High	High	Low (3)
Messenger RNA	Low	Low	High	High	Intermediate	Intermediate	Low (113)
DNA
Mutation	Low	Intermediate	Low	intermediate	Intermediate	Low	High (979)
Methylation	Intermediate	Intermediate	Intermediate	intermediate	Intermediate	Low	Intermediate (387)
Circulating tumour cell	Very low	High	High	Intermediate	Intermediate	No	High (1582)
Protein	High	High	High	High	Low	High	High (15,020)

*Note: Total number of cancer biomarker articles that are published in Pubmed as of 9/13/2021. Pubmed Search Strategy: (serum[ti] OR plasma[ti] OR “non-invasive”[ti] OR “noninvasive”[ti] OR “circulating”[ti] OR “cell free”[ti] OR “liquid biops*“[ti]) AND “Neoplasms”[Mesh] AND “Biomarkers”[Mesh] AND “MicroRNAs”[Mesh]. For other ncRNAs, “MicroRNAs”[Mesh] was replaced by “RNA, Long Noncoding”[Mesh], “RNA, Circular”[Mesh], “RNA, Transfer”[Mesh], “RNA, Messenger”[Mesh], “Mutation”[Mesh], “DNA Methylation”[Mesh], “Neoplastic Cells, Circulating”[Mesh], “Proteins”[Mesh] and (piRNA OR piwi interacting RNA). Reviews, meta-analysis and unrelated publications were excluded from the final count.