The present invention discloses the use of a complement 3a receptor (C3aR) antagonist and a mobilizer of hematopoietic stem cells and/or progenitor cells in methods and compositions for stimulating or enhancing the development, mobilization, proliferation and/or differentiation of a neutrophil-containing leukocyte population that inhibits growth and/or spread of a tumor and for treating or preventing a hyperproliferative cell disorder.