Recent studies on CD9 expression of lung, breast, pancreatic and colon cancers and other malignant tumors and its clinicopathological significance, suggested that CD9 expression was related to tumor metastasis, could inhibit tumor metastasis effect, and, that when the tumor had lymph node or hematogenous metastasis, the CD9 expression level was significantly reduced [9-15,19]. The gene discussed is CD9; the disease is cancer.