MAPK1 and hepatocellular carcinoma: In HCC, HGF derived from M2 TAMs accumulates in HCC cells and activates HGF/c-Met, extracellular signal-regulated kinase 1 (ERK1)/ERK2/mitogen-activated protein kinase (MAPK), and PI3K/Akt signals through a feed-forward control, which in turn attracts M2 TAMs.