I have demonstrated that BRCA1-mutant triple-negative breast cancer (TNBC) cells are highly sensitive to cyclosporine (CsA) and non-immunosuppressive CsA-derivatives (NIM811 or Alisporivir). To determine whether CsA would also be effective in treating BRCA1-mutant TNBC cells in vivo, I set up a pilot study using a preclinical xenograft model to investigate the efficacy of CsA on BRCA1-mutant TNBC cell-derived tumors. Luciferase expressing SUM149PT BRCA1-mutant stably transfectant cells were created by G418 selection. To induce tumor formation, two million cancer cells were injected subcutaneously to each recipient host. Tumors were detected at ~2 week post-injection. Animals were being monitored on a daily basis after cell injection. All animals were scanned once per week by an In Vivo Imaging System (IVIS, PerkinElmer) before and after placebo or CsA treatment. I have administered CsA q2d i.p. to the treatment group and same amount of vehicle to the control group. Animal group transplanted with SUM149PT BRCA1 mutant cancer cells and subsequently treated with cyclosporine (CsA) was initiated on 04/16/2018 and concluded on 06/30/2018. I find that at CsA is effective to suppress and delay the progression of tumor derived from SUM149PT BRCA1 mutant cancer cells