The purpose of this study is to compare progression-free survival (PFS) of patients with advanced, recurrent or metastatic endometrial cancer who have received one, but not more than two, prior lines of chemotherapy either as adjuvant therapy or treatment for advanced disease, and then when treated with ridaforolimus or the investigators' choice of progestin or chemotherapy.

Inclusion Criteria:

• 18 years of age or older
• Endometrial cancer
• Patients must have been treated with at least one line of chemotherapy, but not more than two lines of chemotherapy, and experienced progressive disease
• At least one measurable lesion
• ECOG performance status less than or equal to 1
• Minimum life expectancy of 3 months
• Adequate renal and hepatic function
• Adequate bone marrow function
• Serum cholesterol <350 mg/dL and triglycerides < 400 mg/dL
• Able to understand and give written informed consent
• Females of childbearing potential must have a negative pregnancy test and use approved contraception from screening to 30 days after the last study drug is given

Exclusion Criteria:

• Two lines of chemotherapy for recurrent or metastatic disease
• Chemotherapy for recurrent or metastatic disease administered within six months of adjuvant therapy
• More than two lines of chemotherapy of any type
• Prior therapy with hormonal agents
• Women who are pregnant or lactating
• Presence of brain or other central nervous system metastases
• Prior therapy with rapamycin, rapamycin analogues or tacrolimus or known sensitivity to these agents
• Anticancer treatment (chemotherapy, radiotherapy) within 4 weeks prior to randomization
• Ongoing toxicity associated with prior anticancer therapy
• Inadequate recovery from any prior surgical procedure or having undergone any major surgical procedure within 2 weeks prior to randomization.
• Another primary malignancy within the past five years (except for non-melanoma skin cancer and cervical carcinoma in situ)
• Known Grade 3 or 4 hypersensitivity to macrolide antibiotics
• Significant uncontrolled cardiovascular disease
• Active infection
• Known HIV infection
• Known Hepatitis B or C infection
• Newly diagnosed (within 3 months before enrollment) or poorly controlled Type 1 or 2 diabetes
• Concurrent treatment with immunosuppressive agents
• A requirement for concurrent treatment with medication that strongly induce or inhibit cytochrome P450 (CYP3A)