FN1 and neoplasm: Results: B16F1 melanoma cells, entrapped in the lungs of pFN-competent C57BL/6-Fn(fl/fl)Mx-Cre− mice, were surrounded by a fibrin matrix, CD11b-positive myeloid cells, and Gr-1-positive granulocytes within 1 h of intravenous injection, while homing F4/80-positive macrophages to lung-born tumor cells occurred within 16 h.