Development of tumor PD and surrogate PD biomarkers using phospho flow assay. (a). Gating strategy of tumor and surrogate tissues in pS6 phospho flow study using BMA and PB obtained from myeloma patients. Representative scheme is shown for myeloma tumor cells (CD45-; CD38+; CD138+) in BMA and monocytes (CD45+; CD14+) in PB and BMA. FACS, i.e., fluorescence-activated cell sorting, is a specialized type of flow cytometry. (b and c). GDC-0941 dose-dependent PD response. Patient-derived BMA and PB were treated with GDC-0941 at indicated doses ex vivo for 2 hours. Phospho flow analysis demonstrated the GDC-0941 dose-dependent tumor PD response in histogram (b) and % of pS6 baseline signals in tumor cells and monocytes (c). Data shown are representative of at least three independent studies.