In conclusion, our data demonstrated that miR-146a played an important role in APL cells by increasing cell proliferation and inhibiting cell apoptosis, at least in part via the tumor-suppressor Smad4. miR-146a expression was associated with peripheral WBC counts, Th/Ts ratios, and PML/RARα expression levels in APL patients, suggesting that miR-146a may represent a novel biomarker for APL and could be used to evaluate the effectiveness of chemotherapy for APL. Here, SMAD4 is linked to acute promyelocytic leukemia.