H2AX and cancer: Consistent with our observation in cultured cells, CX-5461 treatment, but not BMH-21, induced H2AX phosphorylation in the xenografts (Figure S2B, demonstrating that, as in other cancers [9, 26], both RNA Pol I inhibitors impair TNBC tumor growth in vivo, and that CX-5461 alone exhibits an off-target activity.