MicroRNAs are small molecules which have recently been discovered in cells. They are known to be responsible for the normal development of cells and when they are disrupted can contribute to the development of cancer. Many previous studies have been done evaluating the expression of microRNAs in normal tissues as well as a wide variety of cancers. Recently, microRNAs from tumor cells have been detected circulating in the blood of patients with cancer. This presents a novel opportunity to use microRNAs in the blood as an early predictor of cancer as well as a marker of response to therapy. No previous studies have been performed evaluating microRNAs in the blood or cerebrospinal fluid of patients with childhood cancers. We propose a feasibility study to evaluate the presence of microRNAs in the blood and cerebrospinal fluid of patients with central nervous system tumors, leukemia and lymphoma who are currently on chemotherapy and undergoing blood draws, lumbar punctures and/or reservoir taps for routine clinical care. If we're able to identify circulating microRNAs in this population of pediatric patients, we will build upon this data in proposing a future study.