The use of venetoclax-based therapies for pediatric patients with relapsed or refractory malignancies is increasingly common outside of the clinical trial setting. For patients who cannot swallow tablets, it is common to crush the tablets and dissolve them in liquid to create a solution. However, no PK data exists in adults or children using crushed tablets dissolved in liquid in this manner, and as a result, the venetoclax exposure with this solution is unknown. Primary Objectives • To determine the pharmacokinetics of venetoclax when commercially available tablets are crushed and dissolved into a solution Secondary Objectives * To evaluate the safety of crushed venetoclax tablets administered as an oral solution * To determine the pharmacokinetics of venetoclax solution in patients receiving concomitant strong and moderate CYP3A inhibitors * To determine potential pharmacokinetic differences based on route of venetoclax solution administration (ie. PO vs NG tube vs G-tube) * To determine the concentration of venetoclax in cerebral spinal fluid when administered as an oral solution