Recovery of hypoxic MM cells in a normoxic environment. (A) Hypoxic MM cells retained a high level of CXCR4 expression after exposure to 1 hour of normoxic levels of oxygen. (B) The decreased expression of CXCR4 in hypoxic MM cells after incubation for 6 hours in medium from normoxic stroma. (C) Increased adhesion properties of hypoxic MM cells after incubation for 6 hours in medium from normoxic stroma. (D) Increased E-cadherin expression in hypoxic MM cells after incubation for 6 hours in medium from normoxic stroma.