X4P-001 is an orally bioavailable CXCR4 antagonist that has demonstrated activity in various tumor models. CXCR4 (C-X-C chemokine receptor type 4) is the receptor for CXCL12 (C-X-C chemokine ligand type 12). CXCL12 has potent chemotactic activity for lymphocytes and MDSCs (myeloid-derived suppressor cells), and is important in homing of hematopoietic stem cells to the bone marrow. CXCR4 is also expressed and active on multiple types of human cancers, including melanoma, ccRCC, and ovarian cancer, and increased expression of CXCR4 on tumor cells has been associated with significantly decreased overall patient survival.