We further demonstrated that in GBM cells, HR repair efficiency decreased significantly after both genetic and pharmacological inhibition of PI3K (Figure S7A,B, Supporting Information); overexpression of PIK3CA partially reversed the decreases in mRNA expression of HR repair‐related molecules BRCA1/2 and RAD51 and the reduction in HR repair efficiency induced by STELB (Figure 6E–G). Here, RAD51 is linked to glioblastoma.