Principal component analysis 3D plot. Principal component analysis of GSE18842, GSE19188 and GSE70880 datasets. (A) Before normalization, these 3 datasets comprising 399 samples and 963 lncRNAs separated completely. (B) After normalization these 3 datasets comprising 287 samples and 963 lncRNAs. GSE19188 and GSE18842 datasets could merge together but GSE70880 was still separate from the other two.