NGF and cancer: Protein-protein interaction networks from String 9.0 showed that there were comprehensive networks for both NTSR1 and GALR1. The majority of these genes were cancer-related genes, which have been reported to play important roles in cancer initiation, progress or therapy, such as S100A9, NGF, TAC1, CCK, FPR2, ADRA1B, and CCL21 in the gene-gene interaction networks (Additional file 1: Figure S4).