['Although operative injury is thought generally to worsen the prognosis of cancer patients, the relevant mechanisms are not yet understood fully. We tested the hypothesis that operative injury induces mobilization and recruitment of bone marrow stem cells, thereby enhancing angiogenesis and accelerating tumor growth.', 'Mice were subjected to an open gastrotomy, and naïve mice were used as controls. The mobilization of bone marrow stem cells was monitored after operation. Using an established tumor model in green fluorescent protein (GFP)(+) bone marrow-transplanted chimera mice, we investigated further whether the mobilized stem cells affected tumor growth.', 'Compared with the control, gastrotomy increased the populations of CD34(+) cells (6.9 ± 4.5 % vs 3.3 ± 0.4%, P < .05) and CD34(+)/Flk-1(+) cells (0.08 ± 0.02% vs 0.05 ± 0.01%, P < .05) in peripheral blood 12 h after operation. Twelve days after operation, the tumor volume almost doubled in mice after gastrotomy compared with control (580 ± 106 mm(3) vs 299 ± 162 mm(3), P < .05). A histologic analysis of tumor tissue revealed that the microvessel density and number of proliferating cells were significantly greater, but those of apoptotic cells were significantly less, in mice after gastrotomy as compared with control. Furthermore, the number of GFP(+) cells found in tumor tissue was significantly greater in mice that underwent gastrotomy than in controls. Some of the stained GFP(+) cells were positive for CD34 and had been incorporated into microvessels. Administration of AMD3100, which is an antagonist of stromal-cell-derived factor (SDF)-1/CXCR4 signaling pathway, inhibited the recruitment of GFP(+) cells and negated completely the acceleration in tumor growth after operation (345 ± 172 mm(3), P < .05).'] Does operative injury accelerate tumor growth by inducing mobilization and recruitment of bone marrow-derived stem cells?