Leflunomide in Previously Treated Metastatic Triple Negative Cancers

Triple negative breast cancer (TNBC) represents about 15% of breast cancers and is characterized by the lack of expression of estrogen receptor (ER), progesterone receptor (PR), and HER-2 non-amplification. Women with TNBC tend to be younger, African American, and BRCA-1 germline carriers. The hallmark of this subtype is early metastatic recurrences with a peak frequency 1-2 years. Prognosis for metastatic TNBC is especially poor with median survival of about 1 year as compared to about 2-4 years with other types of metastatic breast cancer. The primary objective of the phase I part of this study is to determine the safety, tolerability and maximum tolerated dose of leflunomide in women with previously treated TNBC (or ER+ , HER2-neg MBC in Phase I). The primary objective of the phase 2 part of this study is to determine the efficacy of leflunomide in patients with TNBC. Leflunomide, which will be taken daily by mouth, is an inhibitor of dihydroorotate dehydrogenase (DHODH). This proposal will test if DHODH is a novel target for a particular subset of women with metastatic TNBC.