GDC-0853 is modestly cytotoxic to CLL B cells and limits stroma-induced survival. Viability of CLL cells with or without stromal support following 48 hours of BTK inhibitor treatment (N = 9). Cells were treated with 1 µM BTK inhibitor and measured for viability by flow cytometry. Results were normalized to untreated CLL cells in medium. *P ≤ .05; ***P ≤ .001. n.s., not significant.