The purpose of this study is to learn if a new drug, ONC201 can make tumors become smaller or go away completely. Investigators also want to learn if ONC201 can prevent new deposits of cancer from appearing in new places in participants (metastases). A phase 2 study of ONC201 in PC-PG (pheochromocytoma-paraganglioma) and other neuroendocrine tumors will determine whether inhibition of DRD2 (a member of the dopamine receptor family) is safe in unresectable, recurrent, locally advanced, refractory, or metastatic neuroendocrine cancers including PC-PG, desmoplastic small round cell tumor (DSRCT), Ewing sarcoma (PNET) or any other neuroendicrine tumor with a catecholamine or dopamine biomarker or autocrine or paracrine dependence on dopamine including cholangiocarcinoma and adrenal cortical carcinoma.

ONC201 is an investigational (experimental) agent and has a favorable safety profile in phase 1 and early phase 2 clinical trials in advanced cancers. This study design has been chosen to see whether ONC201 is associated with reduction of anti-hypertension medications, safety and significant efficacy against neuroendocrine tumors, especially PC-PG.

Primary Objective To demonstrate objective responses using MRI or CT, and/or PET-CT imaging. The same CT or MRI imaging to assess disease burden at study entry will be compared at week 6 and 3 months. Patients without progression at 3 months will continue treatment and have imaging at 6, 9 and 12 months after study entry. Metabolic response and/or biomarkers will be compared with study entry PET-CT and scans at 6 weeks, 3 months and 12 months.

Secondary Objectives Progression - free Survival: This will be calculated according to Response Evaluation Criteria In Solid Tumors (RECIST) or development of new disease

Overall survival: Overall survival will be determined by email or telephone contact.

Study Design: Phase 2 open-label fixed dose study Metastatic neuroendocrine tumors including PC-PG are rare diseases.

The current recommended phase II dose of 625 mg orally on 2 consecutive days every week will be used. The same imaging at study entry will be used at subsequent time points (CT or MRI for week 6 and 3, 6, 9, and 12 months) Imaging modality choice will be influenced by the quality of prior scans of the subject and will be ordered so clinical comparison is possible.

Because of travel and lodging considerations associated with the COVID-19 pandemic, some information by the study team/PI may be obtained using virtual visits and 2nd read of scans sent to Cleveland Clinic

1. "Subjects must have a unresectable, recurrent, locally advanced, refractory, or metastatic neuroendocrine tumor including pheochromocytoma-paraganglioma (PC-PG), DSRCT, Ewing Sarcoma or PNET, or any neuroendocrine tumor with a catecholamine or dopamine biomarker or autocrine or paracrine dependence on dopamine including cholangiocarcinoma and adrenal cortical carcinoma (ACC).

2. There is no limit on number of prior therapies.

3. Age ≥14 years.

4. Subjects must have normal organ and marrow function as defined below. Studies should be done within 3 weeks prior to enrollment

   • Hemoglobin ≥ 10.0 g/dl

   • Leukocytes ≥ 1500/mcL

   • Absolute neutrophil count ≥ 1,000/mcL

   • Platelet count ≥ 75000/mcL

   • Total bilirubin within 1.5 x normal institutional limits

   • AST (SGOT) ≤ 5 X institutional upper limit of normal

   • ALT (SGPT) ≤ 5 X institutional upper limit of normal

   • Serum Creatinine <3.0mg/dL

     • 5 1 lesion detectable on CT, MRI, 18FDG PET-CT

6 Subjects must have the ability to understand and the willingness to sign a written informed consent document.

7: Karnofsky or if <16 years old Lansky Play Performance status ≥ 60%

1 year