PTEN and neuroblastoma: Oncogenic miR-21 promotes the proliferation and decreased sensitivity to chemotherapy of human NB cells. Ectopic expression of pre-miR-21 lower the level of tumor suppressor PTEN mRNA and protein and in NB cells. Transfection of anti-miR-21 increases the PTEN expression. However, others reported that inhibition of miR-21 did not affect proliferation of NB cells, suggesting that the precise biological functions of miR-21 in NB still warrant further studies.