Patient description: The patient is a 41-year-old man and a known case of Acromegaly who underwent transsphenoidal surgery 4 months ago. He came to the clinic for the follow up lab studies after his primary resection surgery. His lab study shows the IGF-1 level of 4.5 ULN adjusted by sex and age. His random GH level is 4 ug/L. The recent brain MRI confirmed the residual pituitary tumor. His past medical history is only significant for acromegaly due to pituitary adenoma and the recent surgery. After his surgery he takes only vitamin D and multivitamins.

Clinical trial eligibility criteria: eligible ages (years): 1.0-21.0,  Advanced Malignant Solid Neoplasm Ann Arbor Stage III Childhood Non-Hodgkin Lymphoma Ann Arbor Stage IV Childhood Non-Hodgkin Lymphoma Low Grade Glioma Malignant Glioma Recurrent Childhood Central Nervous System Neoplasm Recurrent Childhood Ependymoma Recurrent Childhood Malignant Germ Cell Tumor Recurrent Childhood Non-Hodgkin Lymphoma Recurrent Childhood Rhabdomyosarcoma Recurrent Childhood Soft Tissue Sarcoma Recurrent Ewing Sarcoma/Peripheral Primitive Neuroectodermal Tumor Recurrent Glioma Recurrent Hepatoblastoma Recurrent Langerhans Cell Histiocytosis Recurrent Malignant Solid Neoplasm Recurrent Medulloblastoma Recurrent Neuroblastoma Recurrent Osteosarcoma Refractory Childhood Malignant Germ Cell Tumor Refractory Ependymoma Refractory Ewing Sarcoma/Peripheral Primitive Neuroectodermal Tumor Refractory Glioma Refractory Hepatoblastoma Refractory Langerhans Cell Histiocytosis Refractory Malignant Glioma Refractory Malignant Solid Neoplasm Refractory Medulloblastoma Refractory Neuroblastoma Refractory Non-Hodgkin Lymphoma Refractory Osteosarcoma Refractory Primary Central Nervous System Neoplasm Refractory Rhabdomyosarcoma Refractory Soft Tissue Sarcoma Rhabdoid Tumor Wilms Tumor Patient must have enrolled onto APEC1621SC and must have been given a treatment assignment to Molecular Analysis for Therapy Choice (MATCH) to APEC1621H based on the presence of an actionable mutation Patients must have a body surface area >= 0.65 m^2 at enrollment Patients must have radiographically measurable disease at the time of study enrollment; patients with neuroblastoma who do not have measurable disease but have iobenguane (MIBG) positive (+) evaluable disease are eligible; measurable disease in patients with CNS involvement is defined as tumor that is measurable in two perpendicular diameters on magnetic resonance imaging (MRI) and visible on more than one slice Note: The following do not qualify as measurable disease Malignant fluid collections (e.g., ascites, pleural effusions) Bone marrow infiltration except that detected by MIBG scan for neuroblastoma Lesions only detected by nuclear medicine studies (e.g., bone, gallium or positron emission tomography [PET] scans) except as noted for neuroblastoma Elevated tumor markers in plasma or cerebrospinal fluid (CSF) Previously radiated lesions that have not demonstrated clear progression post radiation Leptomeningeal lesions that do not meet the measurement requirements for Response Evaluation in Solid Tumors (RECIST) 1.1  Pregnant or breast-feeding women will not be entered on this study due to risks of fetal and teratogenic adverse events as seen in animal/human studies; pregnancy tests must be obtained in girls who are post-menarchal; women of child-bearing potential and their partners should agree to use two (2) highly effective forms of contraception throughout study participation and for at least one (1) month after the last dose of olaparib; male study participants should avoid fathering a child or donating sperm during the study and for three (3) months after the last dose of olaparib Concomitant medications Corticosteroids: patients receiving corticosteroids who have not been on a stable or decreasing dose of corticosteroid for at least 7 days prior to enrollment are not eligible; if used to modify immune adverse events related to prior therapy, >= 14 days must have elapsed since last dose of corticosteroid Investigational drugs: patients who are currently receiving another investigational drug are not eligible Anti-cancer agents: patients who are currently receiving other anti-cancer agents are not eligible Anti-GVHD agents post-transplant: patients who are receiving cyclosporine, tacrolimus or other agents to prevent graft-versus-host disease post bone marrow transplant are not eligible for this trial CYP3A/CYP3A4 agents: patients who are currently receiving drugs that are strong and moderate inducers or inhibitors of CYP3A or CYP3A4 are not eligible; strong inducers or inhibitors of CYP3A4 should be avoided from 21 days prior to enrollment to the end of the study Patients who have an uncontrolled infection are not eligible Patient who are known to be serologically positive for human immunodeficiency virus (HIV) Patients with known active hepatitis (i.e. hepatitis B or C)