The purpose of this study is to evaluate the investigational oral drug AMXT 1501 in combination with oral eflornithine (DFMO). An investigational drug is one that has not been approved by the U.S. Food \& Drug Administration (FDA), or any other regulatory authorities around the world for use alone or in combination with any drug, for the condition or illness it is being used to treat.

The goals of this part of the study are:

* Establish a recommended dose of AMXT 1501 in combination with DFMO
* Test the safety and tolerability of AMXT 1501 in combination with DFMO
* To determine the activity of study treatments chosen based on:
* How each subject responds to the study treatment
* How long a subject lives without their disease returning/progressing

This phase III single arm trial determines whether taking prophylactic letermovir will reduce the likelihood of infection with cytomegalovirus (CMV) in children and adolescents after stem cell transplant compared to estimated rate of infection without prophylaxis. The treatments used to prepare for HCT reduce the body's natural infection-fighting ability and increase the likelihood of an infection with a virus called cytomegalovirus. "Prophylaxis" means to take a drug to prevent a disease or side effect. Letermovir is an antiviral drug that stops cytomegalovirus from multiplying and may prevent cytomegalovirus infection and make the disease less severe.

This phase III trial compares the effect of open thoracic surgery (thoracotomy) to thoracoscopic surgery (video-assisted thoracoscopic surgery or VATS) in treating patients with osteosarcoma that has spread to the lung (pulmonary metastases). Open thoracic surgery is a type of surgery done through a single larger incision (like a large cut) that goes between the ribs, opens up the chest, and removes the cancer. Thoracoscopy is a type of chest surgery where the doctor makes several small incisions and uses a small camera to help with removing the cancer. This trial is being done evaluate the two different surgery methods for patients with osteosarcoma that has spread to the lung to find out which is better.

This phase II trial studies the best approach to combine chemotherapy and radiation therapy (RT) based on the patient's response to induction chemotherapy in patients with non-germinomatous germ cell tumors (NGGCT) that have not spread to other parts of the brain or body (localized). This study has 2 goals: 1) optimizing radiation for patients who respond well to induction chemotherapy to diminish spinal cord relapses, 2) utilizing higher dose chemotherapy followed by conventional RT in patients who did not respond to induction chemotherapy. Chemotherapy drugs, such as carboplatin, etoposide, ifosfamide, and thiotepa, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Radiation therapy uses high energy x-rays or high-energy protons to kill tumor cells and shrink tumors. Studies have shown that patients with newly-diagnosed localized NGGCT, whose disease responds well to chemotherapy before receiving radiation therapy, are more likely to be free of the disease for a longer time than are patients for whom the chemotherapy does not efficiently eliminate or reduce the size of the tumor. The purpose of this study is to see how well the tumors respond to induction chemotherapy to decide what treatment to give next. Some patients will be given RT to the spine and a portion of the brain. Others will be given high dose chemotherapy and a stem cell transplant before RT to the whole brain and spine. Giving treatment based on the response to induction chemotherapy may lower the side effects of radiation in some patients and adjust the therapy to a more efficient one for other patients with localized NGGCT.

The purpose of this study is to evaluate the efficacy of digoxin in treating relapsed non-SHH, non-WNT medulloblastoma in pediatric and young adult patients.