The purpose of this study is to test an experimental approach called cell therapy for neuroblastoma or retinoblastoma. This study will take a patient's own white blood cells (T cells) and change them to turn against the cancer. These cells are an experimental treatment and have not been approved by the FDA. CAR T cells have been used to treat other cancers, but GPC2 CAR T cells have not been administered to human patients prior to this clinical trial.

If they choose to participate in this study, active participation will last approximately 12 months. Participants will also be asked to sign consent to a separate long term follow-up protocol to monitor their health for up to 15 years after their last GPC2 CAR T treatment.

This study will assess the safety and effectiveness of GPC2 CAR T cells. Overall, approximately 45 subjects will be enrolled on this study.

The purpose of this research study is to determine if certain markers in your blood are increased over the duration of your chemotherapy, especially as you get sicker, such as developing a severe infection (sepsis) or severe respiratory failure (acute respiratory distress syndrome).

This study has two parts. Part A enrolls patients who have been diagnosed with a solid tumor, lymphoma or desmoid tumor that has either come back ("relapsed") or does not respond to therapy ("is refractory"). Part B enrolls patients with a relapsed or refractory Ewing sarcoma, desmoid tumor, osteosarcoma, liver tumor, Wilms tumor, or tumors with changes in a gene family known as the Wnt pathway. This study involves taking a study drug called tegavivint. The study will be testing different doses of the study drug to find the safest dose.