Combination therapy using leflunomide with checkpoint kinase 1 (CHK1) inhibitors has shown enhanced efficacy in reducing the growth of P53-deficient breast tumors and inducing cell apoptosis compared to treatment with leflunomide alone.108 Furthermore, in a phase I clinical trial aimed at refractory multiple myeloma, leflunomide displayed manageable side effects, with disease stabilization occurring in 9 of the 11 patients (NCT: NCT02509052). Here, CHEK1 is linked to breast neoplasm.