A open-label, multi-center 2-year safety study to ascertain the baseline levels of bone marrow fibers in previously treated adults with chronic immune (idiopathic) thrombocytopenic purpura (ITP) and to evaluate the long-term effect of eltrombopag on bone marrow fibers. The study will also describe the long-term safety and tolerability of oral eltrombopag treatment in subjects with chronic ITP.