RRM2 and small cell lung carcinoma: The utilization of miRNAs as inhibitors or activators is still in the developing stages and needs to be further improved or developed to cope with the undesired or off-target effects; however, our efforts also highlight the possibilities of targeting the CXCR4/FOXM1/RRM2 axis to thwart SCLC growth and metastasis (Fig. 7G).