GAB1 and medulloblastoma: Interestingly, pathway analysis of the known oncogenic downstream marker GRB2-associated-binding protein 1 (GAB-1), which is used to show SHH pathway activation in medulloblastoma, and Stathmin (STMN-1), a downstream marker of the PI3K/AKT/mToR pathway, were positive in three SMO-mutant tumors, suggesting a possible interaction in these parallel oncogenic pathways [23].