Inclusion Criteria:  Age ≥ 18 Advanced or metastatic solid tumor with lack of PTEN expression as determined by immunohistochemistry. Lack of PTEN expression is defined as the absence of staining in the tumor (<5%), with strong positive staining of adjacent normal endometrium or stromal cells, using the monoclonal DAKO antibody 6H2.1.9 Patients must have measurable disease per RECIST 1.1 criteria (Appendix C). Patients must have progressed on, be refractory or intolerant of standard therapy for their cancer, if such a standard therapy exists. Patients with treated brain metastases are eligible if follow-up brain imaging at least 4 weeks after after CNS directed therapy shows no evidence of progression. Patients with new or progressive brain metastases (active brain metastases) or leptomeningeal disease are eligible if the treating physician determines that immediate CNS directed therapy is not required and is unlikely to be required during the first cycle of therapy. ≥ 4 weeks from last systemic therapy, surgery or radiation. ECOG performance status 0-2. Patients with HIV on effective anti-retroviral therapy with an undetectable viral load within 6 months are eligible for this trial.  Adequate organ and marrow function as defined below:  Leukocytes ≥ 3,000/mcL Absolute neutrophil count ≥ 1,000/mcL Platelets ≥ 100,000/mcl Total bilirubin within institutional upper limit of normal. (≤ ULN) AST (SGOT)/ALT (SPGT) ≤ ULN GFR (Cockroft-Gault) ≥ 50 mL/min/1.73m2 Negative serum or urine pregnancy test within 3 days prior to C1D1 of leflunomide therapy. Women of child-bearing potential and men must agree to use adequate contraception before study entry, for the duration of study participation, and for 90 days following completion of therapy Ability to understand and the willingness to sign a written informed consent  Exclusion Criteria:  Patients with primary CNS tumors are not eligible. Patients who have had chemotherapy or radiotherapy within 4 weeks before entering the study or those who have not recovered from grade ≥ 2 adverse events due to agents administered more than 4 weeks earlier. Adverse events such as alopecia, hypothyroidism, and neuropathy are allowed. Other adverse events may be allowed by permission of the principal investigator. Patients may not be receiving any other investigational agents. A known history of acute or chronic Hepatitis B or C, due to the known potential hepatotoxicity of leflunomide. History of allergic reactions attributed to compounds of similar chemical or biologic composition to leflunomide or teriflunomide. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. Patients must not be pregnant or nursing due to the potential for congenital abnormalities and the potential of this regimen to harm nursing infants.