Recently, using multiple genetic lineage tracing in transgenic (GEMM-shP53) and syngeneic GL261 mouse models, Bowman and collaborators have demonstrated that microglia specifically repress Itga4 (CD49D), enabling the distinction between microglia and monocyte-derived macrophages in murine tumours [35] (Figure 1). The gene discussed is ITGA4; the disease is neoplasm.