ITGAM and neoplasm: Tumor-derived factors stimulate resident macrophages at pre-metastatic locations, prompting the recruitment of CD11b + Ly6c-high inflammatory monocytes that gather and evolve into metastasis-associated macrophages.49 Metastasis-associated macrophages assist in circulating tumor cells (CTCs) extravasation, migration through the matrix and the formation of micrometastases.50,51 With the maturation of PMN, CTCs are promoted to infiltrate from blood vessels and attract tumor cells to the niche to actively promote the occurrence of metastasis.