Inclusion Criteria:
* Study participants must have histologically-confirmed metastatic and/or recurrent liposarcoma (limited to the subtypes of well-differentiated and/or dedifferentiated liposarcoma, which are associated with MDM2 amplifications), or myxoid liposarcoma, or CIC-rearranged sarcoma.
* ECOG performance status ≤2
* Adequate organ and marrow function as defined by the following metrics resulted within 7 days of study enrollment:
* WBC \>3000/mm3
* Platelets \>75,000μl
* ANC \>1500μl
* Hgb \>9g/dl
* Creatinine \<1.5 x ULN or measured CrCl of \>60ml/m2/1.73 m2
* Total bilirubin \<2 x ULN
* AST/ALT \<3 x ULN
* Participants must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded for non- nodal lesions and short axis for nodal lesions) as ≥20 mm (≥2 cm) by chest x-ray or as
≥10 mm (≥1 cm) with CT scan, MRI, or calipers by clinical exam. See Section 11 (Measurement of Effect) for the evaluation of measurable disease.
* Patients must have recovered from toxicity related to prior therapy to grade \<=1 (defined by CTCAE v5.0) (except alopecia and neuropathy, or immunotherapy related hypothyroidism)
* As the effect of this study drug on the developing human fetus is not known, women of child-bearing potential and men must agree to use at least 2 methods of contraception (abstinence; hormonal or barrier method of birth control) for the study and at least 2 months after completion.
* Female patient of childbearing potential has a negative serum pregnancy test within 7 days of study enrollment.
* Ability to understand and the willingness to sign a written informed consent document.
* Age ≥18 years
* Patients must have completed all prior anti-cancer treatment for liposarcoma, including radiation, ≥ 14 days prior to registration.
Exclusion Criteria:
* Patient with current evidence of active and uncontrolled infection, NYHA Class III-IV CHF, documented Child's class B-C cirrhosis, or uncontrolled medical disease which in the opinion of the investigator or the sponsor could compromise safety and/or assessment of efficacy.
* Active infection with hepatitis C virus (HCV) or hepatitis B virus (HBV); subjects who are positive for hepatitis B core antibody, hepatitis B surface antigen, or hepatitis C antibody must have a negative PCR result before enrollment; those who are PCR positive will be excluded.
* Major surgical procedure or open surgical biopsy within 28 days of first dose of study drug
* Active central nervous system (CNS) disease involvement, or prior history of NCI CTCAE Grade ≥3 drug-related CNS toxicity. Subject with known CNS metastases that are treated and stable (without evidence of CNS toxicity) and are not requiring systemic steroids are allowed to be enrolled.
* Patient has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial
* Myocardial infarction within 12 months of screening
* Use of any other concurrent investigational agents or anticancer agents, excluding hormonal therapy for breast or prostate cancer
* Pregnant women are excluded from this study because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with BTX- A51, breastfeeding should be discontinued if the mother is treated with BTX-A51.
* Inability to swallow pills or inadequate GI absorption in the opinion of the treating investigator.
