Objective   To study the effect of neurotrophic tyrosine kinase receptor B(TrKB) on in vitro invasiveness of malignant transformed hFOB1.19 cells and the role of TrKB in invasion and metastasis of osteosarcoma.    Methods   Expression of TrKB in malignant transformed hFOB1.19 cells and SaOS2 osteosarcoma cells was detected by RT-PCR and immunofluorescence. Function of TrKB of malignant transformed hFOB1.19 cells was further studied. Malignant transformed hFOB1.19 cells were treated with specific tyrosine kinase inhibitor K252a for 24 h as a treatment group

and untreated malignant transformed hFOB1.19 cells into which DMSO was added served as a control group. Morphology of cells was observed under an inverted phase contrast microscope. Cell invasiveness was detected by Transwell assays. Microfilaments of cells were detected by actin immunofluorescence.    Results   The expression of TrKB was significantly higher in malignant transformed hFOB1.19 cells than in SaOS-2 osteosarcoma cells（P＜0.05）. The cells in treatment group became round

aggregated

and even fused compared to those in control group. The cell invasiveness was significantly lower in treatment group than in control group (P0.01). The microfilaments of cells were shorter and more disordered in arrangement in treatment group than in control group.    Conclusion   High expression level of TrKB in malignant transformed hFOB1.19 cells can increase the in vitro invasiveness of such cells. Blockage of TrKB can decrease the in vitro invasiveness of malignant transformed hFOB1.19 cells by changing their microfilament structure. TrKB may play a positive role in invasion and metastasis of osteosarcoma.