H19 and neoplasm: To further test the hypothesis that plasma lncRNAs were primarily released or leaked from the tumor cells, qPCR analysis was used to measure H19 expression in different five GC cell lines (including four GC cells: 7901, AGS, BGC-823, MKN45, and one normal human gastric epithelial cell line: GES-1), and each cell culture medium which was incubated for 0, 24 h and 48 h.