H2AX and chronic myelogenous leukemia, BCR-ABL1 positive: To investigate whether SETD2 and H3K36me3 deficiency impair the activation of HR repair in advanced‐phase CML, LAMA84 (SETD2/H3K36me3‐proficient) cells before and after SETD2 silencing (Figure 3SB) and KCL22 (SETD2/H3K36me3‐deficient) cells before and after SETD2 transfection (Figure 3SC,D) were studied by immunofluorescence to assess phosphorylated H2AX (a DNA double‐strand break [DSB] marker) and Rad51 (a marker of ongoing HR) foci in steady‐state conditions and after hydrogen peroxide (H2O2) exposure (1 mM for 60 min) or chronic UV exposure.