Table 1.

Literature search strategy for Ovid (Embase and Medline).

ID	Search
1	(ccfDNA OR cfDNA OR cfNA OR ctDNA) [kw,ti,ab]
2	(cell-free DNA OR cell-free serum OR cell free DNA OR cell free serum) [kw,ti,ab]
3	(circulating DNA OR circulating free DNA OR circulating-free DNA OR circulating nucleic acids OR circulating tumo?r DNA) [kw,ti,ab]
4	(free DNA OR free tumo?r DNA) [kw,ti,ab]
5	(plasma DNA OR plasma tumo?r DNA OR ptDNA) [kw,ti,ab]
6	(serum DNA OR serum cell-free OR serum cell free) [kw,ti,ab]
7	1 OR 2 OR 3 OR 4 OR 5 OR 6
8	(neoplasms) [sh,ti,ab]
9	(centrif* OR process* OR spin*) [kw,ti,ab]
10	(extract* OR isolate*) [kw,ti,ab]
11	(quanti* OR measure*) [kw,ti,ab]
12	(sensitiv* OR specific*) [kw,ti,ab]
13	9 AND 10 AND 11 AND 12
14	7 AND 8 AND 13

ab, abstract word; kw, keyword; ti, title word; sh, subject heading (i.e. MeSH); ?, wildcard; *, truncation.