The study was discontinued due to a change in development strategy and not due safety concern.

This is an open-label, multi-center, single-arm, two-period Phase 2 study. The study will investigate the efficacy of Sodium Cridanimod in conjunction with progestin therapy in a population of subjects with recurrent or persistent endometrial cancer, who have failed progestin monotherapy or who have been identified as Progesterone Receptor (PrR) negative. All patients must have endometrial cancer PrR status determined from an archival sample at Screening. The PrR status (positive or negative) will be determined by central laboratory by ImmunoHistoChemistry (IHC) testing.

There are two treatment periods and a follow-up period within the study.

Treatment Period 1 (Progestin Monotherapy): During Treatment Period 1, all subjects determined to be PrR positive will receive progestin monotherapy, megestrol acetate, for up to 24 weeks. Subjects will have an MRI or CT scan after 12 and 24 weeks of progestin monotherapy, with response to treatment being assessed according to RECIST 1.1 criteria. All subjects that achieve disease control confirmed by tumor assessment after Treatment Period 1, will be ineligible to enter Treatment Period 2. These subjects will be terminated from the trial and treated according to local standards of practice, which may include continued progestin therapy.

Subjects determined to be PrR negative at Screening will not enroll into Treatment Period 1. These subjects will enroll directly into Treatment Period 2.

Treatment Period 2 (Combination Treatment): All subjects determined to be PrR negative at Screening and those who received at least 4 weeks of progestin monotherapy and who experienced disease progression at the conclusion of Treatment Period 1 will enter Treatment Period 2 of the study. During Treatment Period 2, subjects will receive Sodium Cridanimod in combination with continued progestin treatment, megestrol acetate. Subjects will receive treatment until disease progression as defined according to RECIST 1.1 criteria, with response assessments performed at 12-week intervals.

Follow-up Period: Once subjects progress during Treatment Period 2, they will return for a Safety Follow-up Visit 4 weeks following the last treatment, and then continue to be followed for an additional 12-month period for overall survival.

Inclusion Criteria:

1. Female patients 18 years of age or older;
2. Histologically confirmed serous carcinoma or endometrioid type of endometrial carcinoma (histological documentation of recurrence is not required);
3. Recurrent or persistent progressive disease which is refractory to curative therapy or established treatments and cannot be treated with surgery or radiotherapy;
4. Measurable disease, as defined by RECIST 1.1 criteria;
5. At least one "target lesion" to be used to assess response, as defined by RECIST 1.1 criteria. Tumors within a previously irradiated field will be designated as "non-target" lesions unless previous progression is documented;
6. Availability of archived tumor tissue sample that can be used for assessment of PrR status by the central laboratory;
7. GOG (Gynecologic Oncology Group) performance status 0-2 (refer to Appendix A);
8. Calculated Glomerular filtration rate ≥ 50 mL/min;
9. Total bilirubin ≤ 2.5 times upper limit of normal (ULN);
10. AST ≤ 2.5 times ULN (≤ 5 times ULN for patients with liver metastases);
11. Alkaline phosphatase ≤ 2.5 times ULN (≤ 5 times ULN for patients with liver metastases);
12. Albumin ≥ 3.0 mg/dL;
13. Ability to take oral medication;
14. Patients able to understand the nature of the study and who are willing to give written informed consent;
15. And for Treatment Period 2 only: 1) Patients participating in Treatment Period 1 must have had disease progression after receiving at least 4 weeks of progestin therapy or 2) Patients must be determined as PrR negative status at Screening.

Exclusion Criteria:

1. Mixed histology of the tumor or evidence of tumor histology other than serous carcinoma or endometrioid type of endometrial carcinoma;
2. Concurrent systemic corticosteroid therapy;
3. Concurrent oral contraceptive use / Women of childbearing potential not using highly effective means of contraception;
4. Pregnancy confirmed by pregnancy test / Lactating women;
5. Prior therapy with hormonal progestin agents;
6. Patients who are candidates for treatment with standard chemotherapy agents (there is no limit to the number of lines of chemotherapy);
7. History of blood clot;
8. History of known bleeding disorder (i.e. disseminated intravascular coagulation or clotting factor deficiency);
9. Major surgery within 4 weeks prior to the start of the study;
10. Patients with clinically significant illnesses which, according to the Investigator, could compromise participation in the study;
11. History of other clinically active malignancies within 5 years, except for carcinoma in situ of the cervix, basal cell carcinoma, or squamous carcinoma of the skin.
12. Known hypersensitivity or idiosyncratic reaction to any of the study drugs (Sodium Cridanimod, megestrol acetate, lidocaine) and excipients;
13. Patients with known brain metastases;
14. Patients currently receiving any other investigational agents;
15. Patients currently receiving any other anticancer therapies;
16. Participation in any other clinical study within the last 4 weeks prior to the start of the study

Females with endometrial cancer