Objective   To investigate the expressions of multi-drug resistance gene (MDR1)

multi-drug resistance-associated protein gene (MRP1)

and lung resistance protein gene (LRP) in the peripheral blood mononuclear cells in chemotherapy children with malignant solid tumors and its relationship with clinical chemotherapy.    Methods   A total of 59 children with malignant solid tumors at an age from 9 months to 14 years old who admitted in our hospital from January 2008 to October 2009 were collected in this study. There were 24 cases of neuroblastoma

16 cases of yolk sac tumor

and 19 cases of lymphoma. Another 30 health age- and sex-matched children served as control. The expressions of MDR1

MRP1 and LRP in the peripheral blood mononuclear cells (PBMCs) before and after chemotherapy

in fresh frozen tumor tissue samples and the in the peripheral blood samples of normal control group were detected by real-time fluorescence quantitative PCR (FQ-PCR).    Results   All MDR1 expression level in the peripheral blood of chemotherapy children was positively correlated with its expression level in the same period tumor tissue samples (r=0.894

P=0.000). There was a negative correlation between the mdr1 mRNA changes and the changes of the tumor size before and after chemotherapy (neuroblastoma: r=-0.733

P=0.000; yolk sac tumor: r=-0.874

P=0.000; lymphoma: r=-0.617

P=0.005). A negative correlation was found between MDR1 mRNA level in peripheral blood before chemotherapy and the changes of corresponding tumor markers after the first time chemotherapy [for neuroblastoma

urine vanillylmandelic acid (VMA): r=-0.440

P=0.046; for yolk sac tumor

alphafetoprotein (AFP): r=-0.831

P=0.000; lymphoma: lactate dehydrogenase (LDH): r=-0.495

P=0.031]. The increased MDR1 mRNA level in peripheral blood of chemotherapy children was related to the increased times of chemotherapy treatments (P0.05).    Conclusion   Dynamically detection for the mdr1 level in PBMCs before and after chemotherapy is valuable for evaluating the treatment response and prognosis in chemotherapy children with malignant solid tumors

and for revising the chemotherapeutic regimen.