Olaparib induces DNA damage and mitotic catastrophe in ATM mutant lymphoid cells. (A) Induction of γH2AX (left) and RAD51 (right) foci after 7 days exposure to 3μM olaparib measured by immunofluorescence. (B) Differential immunofluorescent staining of cells undergoing normal mitosis (positive for H3 ser-10 phosphorylation and negative for Lamin B), mitotic catastrophe (nega-tive for H3 serine-10 and positive for Lamin B), and apoptosis (negative for both H3 serine-10 and Lamin B), shown at original magnification ×500. (C) Induction of mitotic catastrophe determined by immunofluorescence-based morphologic analysis after 72 hours exposure to 3μM olaparib.