Circulating DNA is defined as a kind of extracellular DNA that exists in plasma,cerebrospinal fluid and synovial fluid.The concentration of circulating DNA of cancer patients is significantly higher than that in healthy people.The genetic and epigenetic alterations of circulating cell-free nucleic acids are relevant to cancer development and progression,for example,gene mutation,DNA methylation and microsatellite instability and so on.The quantitative and qualitative detection of circulating DNA shows promising potential value in cancer screening,diagnosis,disease monitoring treatment and prognosis.

Objective: To establish a method for the determination of cinnamic acid in Lingguizhugan Decoction (Poria, Ramuls Cinnamomi, Rhizoma Atractylodis macrocephalae, Radix Glycrrhizae, etc.). Methods: Using RP HPLC with Hypersil C 18 column, methanol acetonitrile water acetic acid (10∶22∶70∶1.4,v/v) as mobile phase, detection wavelength at 254nm and p dimethylaminobenzaldehyde as the internal standard.Results: The mean recovery and RSD were 98.2% and 1.9% ( n =6), respectively, the linear range of cinnamic acid was 8.4～168?g?mL -1 ( r =0.9999). Conclusion: The method is simple, rapid, accurate and reproducible, and may be used for the determination of cinnamic acid in Lingguizhugan Decoction.