ABCG2 increases in patient plasma cells after high-dose chemotherapy and at relapse. (A-B) A patient bone marrow aspirate taken before (A) and during (B) HDC with melphalan and topotecan exhibited an increase in immunofluorescence of ABCG2 (green). (C) This same patient demonstrated an increase in ABCG2 expression by immunofluorescence at relapse as well. (D) ABCG2 protein expression before HDC and at relapse assessed by Western blot in 4 patients on the MTV study. Laser densitometry analysis of the immunoblots shows a 1.54- and 1.94-fold increase in ABCG2 during HDC for patients A and B, respectively, and a 3.68- and 1.34-fold increase in ABCG2 at relapse for patients C and D, respectively. In all cases, this is relative to the pre-HDC ABCG2 protein expression.