This study will evaluate the safety and tolerability of GS-9901 monotherapy in adults with follicular lymphoma (FL), marginal zone lymphoma (MZL), chronic lymphocytic leukemia (CLL), or small lymphocytic lymphoma (SLL). The study will also characterize the pharmacokinetic (PK) profile of GS-9901, determine the appropriate dosing regimen of GS-9901 for use in future clinical trials, and to evaluate the efficacy of GS-9901 monotherapy in adults with FL, MZL, CLL, or SLL.