H2AX and neoplasm: We have previously reported on two validated biomarker assays that are currently being used for correlative studies in the clinical trial of indenoisoquinolines NSC 743400 and NSC 725776: a quantitative immunofluorescence assay for measuring histone H2AX phosphorylated at serine 139 (γH2AX) in tumor biopsies, and an assay to detect γH2AX in circulating tumor cells using the CellSearchTM platform [28]–[30].