RB1 and gastric cancer: p75NTR inhibits gastric cancer proliferation by downregulating cyclin A, cyclin D1, cyclin E, cyclin-dependent kinase 2, p-Rb, and PCNA and inhibits the invasion and metastasis of gastric cancer through downregulating nuclear factor κ B-dependent expression of urokinase-type plasminogen activator and matrix metalloproteinase-943,44.