Specifically, we show that RAP2A, the human homolog of Rap2l, which encodes a Drosophila small GTPase and novel ACD regulator, displays low expression levels in GBM and that restitution of RAP2A in GBM neurosphere cultures increases the ACD and decreases the expression of stem cell markers in the GSCs. The gene discussed is ACD; the disease is glioblastoma.