Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 1.0-30.0,  Hepatoblastoma Previously Treated Childhood Rhabdomyosarcoma Recurrent Childhood Liver Cancer Recurrent Childhood Rhabdomyosarcoma Recurrent Ewing Sarcoma/Peripheral Primitive Neuroectodermal Tumor Recurrent Neuroblastoma Recurrent Osteosarcoma Rhabdomyosarcoma Patients with any of the following tumors who have relapsed or refractory disease are eligible Osteosarcoma Ewing?s sarcoma / peripheral primitive neuroectodermal tumor (PNET) Rhabdomyosarcoma Neuroblastoma (measurable or evaluable disease) Hepatoblastoma Patients must have had histologic verification of malignancy at original diagnosis or relapse Patients must have radiographically measurable disease (with the exception of neuroblastoma) Measurable disease is defined as the presence of at least one lesion on magnetic resonance imaging (MRI) or computed tomography (CT) scan that can be accurately measured with the longest diameter a minimum of 10 mm in at least one dimension (CT scan slice thickness no greater than 5 mm) Note: the following do not qualify as measurable disease  Patients who are pregnant or breast-feeding are not eligible for this study; negative pregnancy tests must be obtained in girls who are post-menarchal; males or females of reproductive potential may not participate unless they have agreed to use an effective contraceptive method for the duration of study therapy; study drug may also potentially be secreted in milk and therefore breastfeeding women are excluded Growth factors that support platelet or white cell number or function must not have been administered within the 7 days prior to enrollment (14 days if pegfilgrastim) Patients requiring corticosteroids who have not been on a stable or decreasing dose of corticosteroid for the 7 days prior to enrollment are not eligible Patients who are currently receiving another investigational drug are not eligible Patients who are currently receiving other anti-cancer agents are not eligible Anti-graft-versus-host disease (GVHD) or agents to prevent organ rejection post-transplant: patients who are receiving cyclosporine, tacrolimus or other agents to prevent either graft-versus-host disease post bone marrow transplant or organ rejection post-transplant are not eligible for this trial Patients who have an uncontrolled infection are not eligible Patients who have received prior treatment with imetelstat are not eligible Patients who in the opinion of the investigator may not be able to comply with the safety monitoring requirements of the study are not eligible Patients with prior allogeneic transplants are not eligible