Metarrestin (ML-246) in Subjects With Metastatic Solid Tumors

Background: Metastasis is the spread of cancer from one organ to a nonadjacent organ. It causes 90% of cancer deaths. No treatment specifically prevents or reduces metastasis. Researchers hope a new drug can help. It stops cancer cells from growing and spreading further and possibly shrink cancer lesions in distant organs. Objective: To find a safe dose of metarrestin and to see if this dose shrinks tumors. Eligibility: Adults age 18 and older with pancreatic cancer, breast cancer, or a solid tumor that has not been cured by standard therapies. Also, children age 12-17 with a solid tumor (other than a muscle tumor) with no standard therapy options. Design: Participants will be screened with: * blood tests * physical exam * documentation of disease confirmation or tumor biopsy * electrocardiogram to evaluate the heart * review of their medicines and their ability to do their normal activities Participants will take metarrestin by mouth until they cannot tolerate it or stop to benefit from it. They will keep a medicine diary. Participants will visit the Clinical Center. During the first month there are two brief hospital stays required with visits weekly or every other week thereafter. They will repeat some of the screening tests. They will fill out questionnaires. They will have tests of their cognitive function. They will have an electroencephalogram to record brain activity. They will have a computed tomography (CT) scan or magnetic resonance imaging (MRI). A CT is a series of X-rays of the body. An MRI uses magnets and radio waves to take pictures of the body. Adult participants may have tumor biopsies. Participants will have a follow-up visit 30 days after treatment ends. Then they will have follow-up phone calls or emails every 6 months for the rest of their life or until the study ends.

* INCLUSION CRITERIA: * Adult (\>= 18 years) subjects with: * histologically or cytologically confirmed solid tumors (Phase IA). OR --histologically or cytologically confirmed pancreatic, colorectal, or breast cancer (Phase IB) OR * Pediatric (\>=12 and \< 18 years) subjects with histologically or cytologically confirmed solid tumors other than rhabdomyosarcoma (RMS) including embryonal, alveolar, spindle cell/sclerosing and pleomorphic subtypes of RMS (Phase IB). * Subjects must have disease that: * is not amenable to potentially curative resection, * spread at least to one other organ system other than primary tumor or recurred after removal of primary tumor * has site measurable per RECIST 1.1 (Phase IB only). * progressed on or after at least one line of standard systemic chemotherapy (Phase IA and IB1) * have no standard therapy option available (Phase IB2) * Patients must have recovered from any acute toxicity related to prior therapy or surgery or disease to a grade 1 or less. * Performance status * Karnofsky \>= 70% (for patients \>= 16 years old), Lansky \>= 70% (for patients \= 1.0 x 10(9)/L, * transfusion-independent platelet count \>= 100 x 10(9)/L, * Hgb \>= 9 g/ dL (patients who have received \= 12 and \< 18 years old). * Ability of subject or parent/guardian to understand and the willingness to sign a written informed consent document. * Subjects must have lesion(s) accessible for biopsy (other than used for measurement of disease) and be willing to undergo mandatory study biopsies (Cohort IB1 only). * Ability to swallow oral capsules. EXCLUSION CRITERIA: * Anticancer treatment within designated period before treatment initiation including: * minor surgical procedure (such as biliary stenting) within 14 days. Note: if liver function tests after biliary stenting or renal function tests after ureteral stenting return to normal, within 5 days after biliary or ureteral stenting; * major surgical procedure or curative radiation treatment within 28 days; * palliative radiation treatment within 14 days; * chemotherapy or experimental drug treatment with published half-life known to be 72 hours or less within 14 days; * experimental drug treatment with unpublished or half-life greater than 72 hours within 28 days; * chemotherapy regimen containing an alkylating antineoplastic agent (cyclophosphamide, chlorambucil, melphalan, or ifosfamide), alkylating-like (platinumbased chemotherapeutic drugs, platinum analogues), and non-classical alkylating agent (dacarbazine, temozolomide) within 28 days. * Patients receiving any medications or substances that are moderate and strong inhibitors or inducers of CYP3A4 and are not able to safely stop these medications are excluded from this study; patients must stop strong CYP3A4 inhibiting/inducing medications within 5 published half-lives and moderate within 3 published half-lives prior to the treatment initiation. Note: dihydropyridine calcium - channel blockers are permitted for management of underling disease. * Subjects with cardiomyopathy diagnosed within 6 months prior to treatment initiation including but not limited to the following: * hypertrophic cardiomyopathy * arrhythmogenic right ventricular cardiomyopathy * abnormal ejection fraction (echocardiogram \[ECHO\]) \