Fibrocytes that were identified in lung tumors as CD45+CD44+CD162+CD11b+F4/80+CCR2/5+CD9+ cells had lost the monocyte marker Ly6C compared to bone marrow fibrocytes, indicating a maturation process in the cancer microenvironment, reminiscent of monocyte to macrophage differentiation in tumors (Fig. 2D, E). This evidence concerns the gene CD9 and cancer.